diff --git a/Cargo.lock b/Cargo.lock
index 6e580bf..53be692 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -74,12 +74,11 @@ name = "chessfriend_core"
 version = "0.1.0"
 
 [[package]]
-name = "chessfriend_move_generator"
+name = "chessfriend_moves"
 version = "0.1.0"
 dependencies = [
  "chessfriend_bitboard",
  "chessfriend_core",
- "chessfriend_position",
 ]
 
 [[package]]
@@ -88,6 +87,7 @@ version = "0.1.0"
 dependencies = [
  "chessfriend_bitboard",
  "chessfriend_core",
+ "chessfriend_moves",
 ]
 
 [[package]]
@@ -172,6 +172,7 @@ name = "explorer"
 version = "0.1.0"
 dependencies = [
  "chessfriend_core",
+ "chessfriend_moves",
  "chessfriend_position",
  "clap",
  "rustyline",
diff --git a/Cargo.toml b/Cargo.toml
index b490c8e..490ec43 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,6 +3,7 @@ members = [
     "bitboard",
     "core",
     "explorer",
+    "moves",
     "position",
 ]
 resolver = "2"
diff --git a/core/src/coordinates.rs b/core/src/coordinates.rs
index 68ff3fe..54aeb1a 100644
--- a/core/src/coordinates.rs
+++ b/core/src/coordinates.rs
@@ -1,5 +1,6 @@
 // Eryn Wells <eryn@erynwells.me>
 
+use crate::Color;
 use std::fmt;
 use std::str::FromStr;
 
@@ -168,6 +169,16 @@ impl Rank {
     /// assert_eq!(Rank::PAWN_STARTING_RANKS[Color::Black as usize], Rank::SEVEN);
     /// ```
     pub const PAWN_STARTING_RANKS: [Rank; 2] = [Rank::TWO, Rank::SEVEN];
+
+    pub const PAWN_DOUBLE_PUSH_TARGET_RANKS: [Rank; 2] = [Rank::FOUR, Rank::FIVE];
+
+    pub fn is_pawn_starting_rank(&self, color: Color) -> bool {
+        self == &Self::PAWN_STARTING_RANKS[color as usize]
+    }
+
+    pub fn is_pawn_double_push_target_rank(&self, color: Color) -> bool {
+        self == &Self::PAWN_DOUBLE_PUSH_TARGET_RANKS[color as usize]
+    }
 }
 
 #[rustfmt::skip]
diff --git a/explorer/Cargo.toml b/explorer/Cargo.toml
index 3281cf4..9689332 100644
--- a/explorer/Cargo.toml
+++ b/explorer/Cargo.toml
@@ -7,6 +7,7 @@ edition = "2021"
 
 [dependencies]
 chessfriend_core = { path = "../core" }
+chessfriend_moves = { path = "../moves" }
 chessfriend_position = { path = "../position" }
 clap = { version = "4.4.12", features = ["derive"] }
 rustyline = "13.0.0"
diff --git a/explorer/src/main.rs b/explorer/src/main.rs
index 8edb00e..5b8a17d 100644
--- a/explorer/src/main.rs
+++ b/explorer/src/main.rs
@@ -1,5 +1,8 @@
+// Eryn Wells <eryn@erynwells.me>
+
 use chessfriend_core::{Color, Piece, PlacedPiece, Shape, Square};
-use chessfriend_position::{fen::ToFen, MakeMoveBuilder, MoveBuilder, Position, PositionBuilder};
+use chessfriend_moves::Builder as MoveBuilder;
+use chessfriend_position::{fen::ToFen, MakeMoveBuilder, Position, PositionBuilder};
 use clap::{Arg, Command};
 use rustyline::error::ReadlineError;
 use rustyline::DefaultEditor;
@@ -97,16 +100,15 @@ fn respond(line: &str, state: &mut State) -> Result<CommandResult, String> {
             )
             .map_err(|_| "Error: invalid square specifier")?;
 
-            let mv = MoveBuilder::new(
-                Piece::new(state.position.player_to_move(), shape),
-                from_square,
-                to_square,
-            )
-            .build();
+            let mv = MoveBuilder::new()
+                .from(from_square)
+                .to(to_square)
+                .build()
+                .map_err(|err| format!("Error: cannot build move: {:?}", err))?;
 
             state.position = MakeMoveBuilder::new(&state.position)
                 .make(&mv)
-                .map_err(|err| format!("error: Cannot make move: {:?}", err))?
+                .map_err(|err| format!("Error: cannot make move: {:?}", err))?
                 .build();
             state.builder = PositionBuilder::from_position(&state.position);
         }
diff --git a/moves/Cargo.toml b/moves/Cargo.toml
new file mode 100644
index 0000000..3c9e6cf
--- /dev/null
+++ b/moves/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "chessfriend_moves"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+chessfriend_core = { path = "../core" }
+chessfriend_bitboard = { path = "../bitboard" }
diff --git a/moves/src/builder.rs b/moves/src/builder.rs
new file mode 100644
index 0000000..5f02364
--- /dev/null
+++ b/moves/src/builder.rs
@@ -0,0 +1,395 @@
+// Eryn Wells <eryn@erynwells.me>
+
+use crate::{castle, defs::Kind, EnPassant, Move, PromotionShape};
+use chessfriend_core::{Color, File, PlacedPiece, Rank, Square};
+use std::result::Result as StdResult;
+
+pub type Result = std::result::Result<Move, Error>;
+type EncodedMoveResult = std::result::Result<u16, Error>;
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum Error {
+    MissingOriginSquare,
+    MissingTargetSquare,
+    MissingCaptureSquare,
+    InvalidEnPassantSquare,
+}
+
+pub trait Style {
+    fn origin_square(&self) -> Option<Square> {
+        None
+    }
+
+    fn target_square(&self) -> Option<Square> {
+        None
+    }
+
+    fn into_move_bits(&self) -> EncodedMoveResult {
+        let origin_square = self.origin_square().ok_or(Error::MissingOriginSquare)?;
+        let target_square = self.target_square().ok_or(Error::MissingTargetSquare)?;
+
+        Ok(self._build_move_bits(origin_square, target_square))
+    }
+
+    unsafe fn into_move_bits_unchecked(&self) -> u16 {
+        let origin_square = self.origin_square().unwrap();
+        let target_square = self.target_square().unwrap();
+
+        self._build_move_bits(origin_square, target_square)
+    }
+
+    fn _build_move_bits(&self, origin_square: Square, target_square: Square) -> u16 {
+        (origin_square as u16 & 0b111111) << 4 | (target_square as u16 & 0b111111) << 10
+    }
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Builder<S: Style> {
+    style: S,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Null;
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Push {
+    from: Option<Square>,
+    to: Option<Square>,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct DoublePush {
+    from: Square,
+    to: Square,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Capture {
+    push: Push,
+    capture: Option<Square>,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct EnPassantCapture {
+    push: Push,
+    capture: Option<EnPassant>,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Promotion<S> {
+    style: S,
+    promotion: PromotionShape,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Castle {
+    color: Color,
+    castle: castle::Castle,
+}
+
+impl EnPassantCapture {
+    fn _build_move_bits(&self, origin_square: Square, target_square: Square) -> u16 {
+        (origin_square as u16 & 0b111111) << 4 | (target_square as u16 & 0b111111) << 10
+    }
+}
+
+impl Style for Null {}
+
+impl Style for Push {
+    fn origin_square(&self) -> Option<Square> {
+        self.from
+    }
+
+    fn target_square(&self) -> Option<Square> {
+        self.to
+    }
+}
+
+impl Style for Capture {
+    fn origin_square(&self) -> Option<Square> {
+        self.push.from
+    }
+
+    fn target_square(&self) -> Option<Square> {
+        self.push.to
+    }
+}
+
+impl Style for Castle {
+    fn origin_square(&self) -> Option<Square> {
+        let parameters = self.castle.parameters(self.color);
+        Some(parameters.king_origin_square())
+    }
+
+    fn target_square(&self) -> Option<Square> {
+        let parameters = self.castle.parameters(self.color);
+        Some(parameters.king_target_square())
+    }
+}
+
+impl Style for DoublePush {
+    fn origin_square(&self) -> Option<Square> {
+        Some(self.from)
+    }
+
+    fn target_square(&self) -> Option<Square> {
+        Some(self.to)
+    }
+
+    fn into_move_bits(&self) -> StdResult<u16, Error> {
+        Ok(Kind::DoublePush as u16
+            | (self.from as u16 & 0b111111) << 4
+            | (self.to as u16 & 0b111111) << 10)
+    }
+}
+
+impl Style for EnPassantCapture {
+    fn origin_square(&self) -> Option<Square> {
+        self.push.from
+    }
+
+    fn target_square(&self) -> Option<Square> {
+        self.push.to
+    }
+
+    fn into_move_bits(&self) -> EncodedMoveResult {
+        let origin_square = self.origin_square().ok_or(Error::MissingOriginSquare)?;
+        let target_square = self.target_square().ok_or(Error::MissingTargetSquare)?;
+
+        Ok(self._build_move_bits(origin_square, target_square))
+    }
+}
+
+impl Style for Promotion<Push> {
+    fn origin_square(&self) -> Option<Square> {
+        self.style.from
+    }
+
+    fn target_square(&self) -> Option<Square> {
+        self.style.to
+    }
+}
+
+impl Style for Promotion<Capture> {
+    fn origin_square(&self) -> Option<Square> {
+        self.style.push.from
+    }
+
+    fn target_square(&self) -> Option<Square> {
+        self.style.push.to
+    }
+}
+
+impl Promotion<Push> {
+    fn into_move_bits(&self) -> StdResult<u16, Error> {
+        let origin_square = self
+            .style
+            .origin_square()
+            .ok_or(Error::MissingOriginSquare)? as u16;
+        let target_square = self
+            .style
+            .target_square()
+            .ok_or(Error::MissingTargetSquare)? as u16;
+
+        Ok(Kind::Promotion as u16
+            | self.promotion as u16
+            | (origin_square & 0b111111) << 4
+            | (target_square & 0b111111) << 10)
+    }
+}
+
+impl Promotion<Capture> {
+    fn into_move_bits(&self) -> StdResult<u16, Error> {
+        let origin_square = self
+            .style
+            .origin_square()
+            .ok_or(Error::MissingOriginSquare)? as u16;
+        let target_square = self
+            .style
+            .target_square()
+            .ok_or(Error::MissingTargetSquare)? as u16;
+
+        Ok(Kind::CapturePromotion as u16
+            | self.promotion as u16
+            | (origin_square & 0b111111) << 4
+            | (target_square & 0b111111) << 10)
+    }
+}
+
+impl Builder<Null> {
+    pub fn new() -> Self {
+        Self { style: Null }
+    }
+
+    pub fn push(piece: &PlacedPiece) -> Builder<Push> {
+        Builder {
+            style: Push {
+                from: Some(piece.square()),
+                to: None,
+            },
+        }
+    }
+
+    pub fn double_push(file: File, color: Color) -> Builder<DoublePush> {
+        let (from, to) = match color {
+            Color::White => (
+                Square::from_file_rank(file, Rank::TWO),
+                Square::from_file_rank(file, Rank::FOUR),
+            ),
+            Color::Black => (
+                Square::from_file_rank(file, Rank::SEVEN),
+                Square::from_file_rank(file, Rank::FIVE),
+            ),
+        };
+
+        Builder {
+            style: DoublePush { from, to },
+        }
+    }
+
+    pub fn castling(color: Color, castle: castle::Castle) -> Builder<Castle> {
+        Builder {
+            style: Castle { color, castle },
+        }
+    }
+
+    pub fn capturing_piece(piece: &PlacedPiece, capturing: &PlacedPiece) -> Builder<Capture> {
+        Self::push(piece).capturing_piece(&capturing)
+    }
+
+    pub fn from(&self, square: Square) -> Builder<Push> {
+        Builder {
+            style: Push {
+                from: Some(square),
+                to: None,
+            },
+        }
+    }
+
+    pub fn build(&self) -> Move {
+        Move(0)
+    }
+}
+
+impl Builder<Push> {
+    pub fn from(&mut self, square: Square) -> &mut Self {
+        self.style.from = Some(square);
+        self
+    }
+
+    pub fn to(&mut self, square: Square) -> &mut Self {
+        self.style.to = Some(square);
+        self
+    }
+
+    pub fn capturing_on(&self, square: Square) -> Builder<Capture> {
+        let mut style = self.style.clone();
+        style.to = Some(square);
+
+        Builder {
+            style: Capture {
+                push: style,
+                capture: Some(square),
+            },
+        }
+    }
+
+    pub fn capturing_en_passant_on(&self, target_square: Square) -> Builder<EnPassantCapture> {
+        match EnPassant::from_target_square(target_square) {
+            Some(en_passant) => {
+                let mut style = self.style.clone();
+                style.to = Some(en_passant.target_square());
+
+                Builder {
+                    style: EnPassantCapture {
+                        push: style,
+                        capture: Some(en_passant),
+                    },
+                }
+            }
+            None => todo!(),
+        }
+    }
+
+    pub fn capturing_piece(&self, piece: &PlacedPiece) -> Builder<Capture> {
+        Builder {
+            style: Capture {
+                push: self.style.clone(),
+                capture: Some(piece.square()),
+            },
+        }
+    }
+
+    pub fn promoting_to(&self, shape: PromotionShape) -> Builder<Promotion<Push>> {
+        Builder {
+            style: Promotion {
+                style: self.style.clone(),
+                promotion: shape,
+            },
+        }
+    }
+
+    pub fn build(&self) -> Result {
+        Ok(Move(Kind::Quiet as u16 | self.style.into_move_bits()?))
+    }
+}
+
+impl Builder<Castle> {
+    fn bits(&self) -> u16 {
+        let bits = match self.style.castle {
+            castle::Castle::KingSide => Kind::KingSideCastle,
+            castle::Castle::QueenSide => Kind::QueenSideCastle,
+        };
+
+        bits as u16
+    }
+
+    pub fn build(&self) -> Result {
+        Ok(Move(self.bits() | self.style.into_move_bits()?))
+    }
+}
+
+impl Builder<Capture> {
+    pub fn promoting_to(self, shape: PromotionShape) -> Builder<Promotion<Capture>> {
+        Builder {
+            style: Promotion {
+                style: self.style,
+                promotion: shape,
+            },
+        }
+    }
+
+    pub fn build(&self) -> Result {
+        Ok(Move(Kind::Capture as u16 | self.style.into_move_bits()?))
+    }
+}
+
+impl Builder<DoublePush> {
+    pub fn build(&self) -> Result {
+        Ok(Move(Kind::DoublePush as u16 | self.style.into_move_bits()?))
+    }
+}
+
+impl Builder<EnPassantCapture> {
+    pub unsafe fn build_unchecked(&self) -> Move {
+        Move(Kind::EnPassantCapture as u16 | self.style.into_move_bits_unchecked())
+    }
+
+    pub fn build(&self) -> Result {
+        Ok(Move(
+            Kind::EnPassantCapture as u16 | self.style.into_move_bits()?,
+        ))
+    }
+}
+
+impl Builder<Promotion<Push>> {
+    pub fn build(&self) -> Result {
+        Ok(Move(self.style.into_move_bits()?))
+    }
+}
+
+impl Builder<Promotion<Capture>> {
+    pub fn build(&self) -> Result {
+        Ok(Move(self.style.into_move_bits()?))
+    }
+}
diff --git a/moves/src/castle.rs b/moves/src/castle.rs
new file mode 100644
index 0000000..731f25f
--- /dev/null
+++ b/moves/src/castle.rs
@@ -0,0 +1,121 @@
+// Eryn Wells <eryn@erynwells.me>
+
+use chessfriend_bitboard::BitBoard;
+use chessfriend_core::{Color, Square};
+
+#[repr(u8)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub enum Castle {
+    KingSide = 0,
+    QueenSide = 1,
+}
+
+pub struct Parameters {
+    /// Origin squares of the king and rook.
+    origin_squares: Squares,
+
+    /// Target or destination squares for the king and rook.
+    target_squares: Squares,
+
+    /// The set of squares that must be clear of any pieces in order to perform this castle.
+    clear_squares: BitBoard,
+
+    /// The set of squares that must not be attacked in order to perform this castle.
+    check_squares: BitBoard,
+}
+
+impl Parameters {
+    pub fn king_origin_square(&self) -> Square {
+        self.origin_squares.king
+    }
+
+    pub fn rook_origin_square(&self) -> Square {
+        self.origin_squares.rook
+    }
+
+    pub fn king_target_square(&self) -> Square {
+        self.target_squares.king
+    }
+
+    pub fn rook_target_square(&self) -> Square {
+        self.target_squares.rook
+    }
+
+    pub fn clear_squares(&self) -> &BitBoard {
+        &self.clear_squares
+    }
+
+    pub fn check_squares(&self) -> &BitBoard {
+        &self.check_squares
+    }
+}
+
+#[derive(Debug)]
+struct Squares {
+    king: Square,
+    rook: Square,
+}
+
+impl Castle {
+    pub const ALL: [Castle; 2] = [Castle::KingSide, Castle::QueenSide];
+
+    /// Parameters for each castling move, organized by color and board-side.
+    const PARAMETERS: [[Parameters; 2]; 2] = [
+        [
+            Parameters {
+                origin_squares: Squares {
+                    king: Square::E1,
+                    rook: Square::H1,
+                },
+                target_squares: Squares {
+                    king: Square::G1,
+                    rook: Square::F1,
+                },
+                clear_squares: BitBoard::new(0b01100000),
+                check_squares: BitBoard::new(0b01110000),
+            },
+            Parameters {
+                origin_squares: Squares {
+                    king: Square::E1,
+                    rook: Square::A1,
+                },
+                target_squares: Squares {
+                    king: Square::C1,
+                    rook: Square::D1,
+                },
+                clear_squares: BitBoard::new(0b00001110),
+                check_squares: BitBoard::new(0b00011100),
+            },
+        ],
+        [
+            Parameters {
+                origin_squares: Squares {
+                    king: Square::E8,
+                    rook: Square::H8,
+                },
+                target_squares: Squares {
+                    king: Square::G8,
+                    rook: Square::F8,
+                },
+                clear_squares: BitBoard::new(0b01100000 << 8 * 7),
+                check_squares: BitBoard::new(0b01110000 << 8 * 7),
+            },
+            Parameters {
+                origin_squares: Squares {
+                    king: Square::E8,
+                    rook: Square::A8,
+                },
+                target_squares: Squares {
+                    king: Square::C8,
+                    rook: Square::D8,
+                },
+                clear_squares: BitBoard::new(0b00001110 << 8 * 7),
+                check_squares: BitBoard::new(0b00011100 << 8 * 7),
+            },
+        ],
+    ];
+
+    pub fn parameters(&self, color: Color) -> &'static Parameters {
+        &Castle::PARAMETERS[color as usize][*self as usize]
+    }
+}
diff --git a/moves/src/defs.rs b/moves/src/defs.rs
new file mode 100644
index 0000000..337f30e
--- /dev/null
+++ b/moves/src/defs.rs
@@ -0,0 +1,34 @@
+// Eryn Wells <eryn@erynwells.me>
+
+use chessfriend_core::Shape;
+
+pub(crate) enum Kind {
+    Quiet = 0b0000,
+    DoublePush = 0b0001,
+    KingSideCastle = 0b0010,
+    QueenSideCastle = 0b0011,
+    Capture = 0b0100,
+    EnPassantCapture = 0b0101,
+    Promotion = 0b1000,
+    CapturePromotion = 0b1100,
+}
+
+#[repr(u16)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub enum PromotionShape {
+    Knight = 0b00,
+    Bishop = 0b01,
+    Rook = 0b10,
+    Queen = 0b11,
+}
+
+impl From<PromotionShape> for Shape {
+    fn from(value: PromotionShape) -> Self {
+        match value {
+            PromotionShape::Knight => Shape::Knight,
+            PromotionShape::Bishop => Shape::Bishop,
+            PromotionShape::Rook => Shape::Rook,
+            PromotionShape::Queen => Shape::Queen,
+        }
+    }
+}
diff --git a/moves/src/en_passant.rs b/moves/src/en_passant.rs
new file mode 100644
index 0000000..49e88a6
--- /dev/null
+++ b/moves/src/en_passant.rs
@@ -0,0 +1,51 @@
+// Eryn Wells <eryn@erynwells.me>
+
+use chessfriend_core::{Rank, Square};
+
+/// En passant information.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct EnPassant {
+    target: Square,
+    capture: Square,
+}
+
+impl EnPassant {
+    fn _capture_square(target: Square) -> Option<Square> {
+        let (file, rank) = target.file_rank();
+        match rank {
+            Rank::THREE => Some(Square::from_file_rank(file, Rank::FOUR)),
+            Rank::SIX => Some(Square::from_file_rank(file, Rank::FIVE)),
+            _ => None,
+        }
+    }
+
+    /// Return en passant information for a particular target square. The target
+    /// square is the square a pawn capturing en passant will move to.
+    ///
+    /// Return `None` if the square is not eligible for en passant.
+    ///
+    /// ## Examples
+    ///
+    /// ```
+    /// use chessfriend_core::Square;
+    /// use chessfriend_moves::EnPassant;
+    /// assert!(EnPassant::from_target_square(Square::E3).is_some());
+    /// assert!(EnPassant::from_target_square(Square::B4).is_none());
+    /// ```
+    pub fn from_target_square(target: Square) -> Option<Self> {
+        match Self::_capture_square(target) {
+            Some(capture) => Some(Self { target, capture }),
+            None => None,
+        }
+    }
+
+    /// The square the capturing piece will move to.
+    pub fn target_square(&self) -> Square {
+        self.target
+    }
+
+    /// The square on which the captured pawn sits.
+    pub fn capture_square(&self) -> Square {
+        self.capture
+    }
+}
diff --git a/moves/src/lib.rs b/moves/src/lib.rs
new file mode 100644
index 0000000..297f82e
--- /dev/null
+++ b/moves/src/lib.rs
@@ -0,0 +1,15 @@
+// Eryn Wells <eryn@erynwells.me>
+
+pub mod testing;
+
+mod builder;
+mod castle;
+mod defs;
+mod en_passant;
+mod moves;
+
+pub use builder::{Builder, Error as BuildMoveError, Result as BuildMoveResult};
+pub use castle::Castle;
+pub use defs::PromotionShape;
+pub use en_passant::EnPassant;
+pub use moves::Move;
diff --git a/moves/src/moves.rs b/moves/src/moves.rs
new file mode 100644
index 0000000..5348306
--- /dev/null
+++ b/moves/src/moves.rs
@@ -0,0 +1,135 @@
+// Eryn Wells <eryn@erynwells.me>
+
+use crate::{castle::Castle, defs::Kind};
+use chessfriend_core::{Rank, Shape, Square};
+use std::fmt;
+
+/// A single player's move. In chess parlance, this is a "ply".
+#[derive(Clone, Copy, Eq, Hash, PartialEq)]
+pub struct Move(pub(crate) u16);
+
+impl Move {
+    pub fn origin_square(&self) -> Square {
+        ((self.0 >> 4) & 0b111111).try_into().unwrap()
+    }
+
+    pub fn target_square(&self) -> Square {
+        (self.0 >> 10).try_into().unwrap()
+    }
+
+    pub fn capture_square(&self) -> Option<Square> {
+        if self.is_en_passant() {
+            let target_square = self.target_square();
+            return Some(match target_square.rank() {
+                Rank::THREE => Square::from_file_rank(target_square.file(), Rank::FOUR),
+                Rank::SIX => Square::from_file_rank(target_square.file(), Rank::FIVE),
+                _ => unreachable!(),
+            });
+        }
+
+        if self.is_capture() {
+            return Some(self.target_square());
+        }
+
+        None
+    }
+
+    pub fn is_quiet(&self) -> bool {
+        self.flags() == Kind::Quiet as u16
+    }
+
+    pub fn is_double_push(&self) -> bool {
+        self.flags() == Kind::DoublePush as u16
+    }
+
+    pub fn is_castle(&self) -> bool {
+        self.castle().is_some()
+    }
+
+    pub fn castle(&self) -> Option<Castle> {
+        match self.flags() {
+            0b0010 => Some(Castle::KingSide),
+            0b0011 => Some(Castle::QueenSide),
+            _ => None,
+        }
+    }
+
+    pub fn is_capture(&self) -> bool {
+        (self.0 & 0b0100) != 0
+    }
+
+    pub fn is_en_passant(&self) -> bool {
+        self.flags() == 0b0101
+    }
+
+    pub fn is_promotion(&self) -> bool {
+        (self.0 & 0b1000) != 0
+    }
+
+    pub fn promotion(&self) -> Option<Shape> {
+        if !self.is_promotion() {
+            return None;
+        }
+
+        Some(match self.special() {
+            0b00 => Shape::Knight,
+            0b01 => Shape::Bishop,
+            0b10 => Shape::Rook,
+            0b11 => Shape::Queen,
+            _ => unreachable!(),
+        })
+    }
+
+    #[inline]
+    fn flags(&self) -> u16 {
+        self.0 & 0b1111
+    }
+
+    #[inline]
+    fn special(&self) -> u16 {
+        self.0 & 0b11
+    }
+
+    fn _transfer_char(&self) -> char {
+        if self.is_capture() || self.is_en_passant() {
+            'x'
+        } else {
+            '-'
+        }
+    }
+}
+
+impl fmt::Display for Move {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if let Some(castle) = self.castle() {
+            match castle {
+                Castle::KingSide => return write!(f, "0-0"),
+                Castle::QueenSide => return write!(f, "0-0-0"),
+            }
+        }
+
+        write!(
+            f,
+            "{}{}{}",
+            self.origin_square(),
+            self._transfer_char(),
+            self.target_square()
+        )?;
+
+        if let Some(promotion) = self.promotion() {
+            write!(f, "={}", promotion)?;
+        } else if self.is_en_passant() {
+            write!(f, " e.p.")?;
+        }
+
+        Ok(())
+    }
+}
+
+impl fmt::Debug for Move {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("Move")
+            .field(&format_args!("{:08b}", &self.0))
+            .finish()
+    }
+}
diff --git a/moves/src/testing.rs b/moves/src/testing.rs
new file mode 100644
index 0000000..b298d5d
--- /dev/null
+++ b/moves/src/testing.rs
@@ -0,0 +1,17 @@
+// Eryn Wells <eryn@erynwells.me>
+
+use crate::BuildMoveError;
+
+pub type TestResult = Result<(), TestError>;
+
+#[derive(Debug, Eq, PartialEq)]
+pub enum TestError {
+    BuildMove(BuildMoveError),
+    NoLegalMoves,
+}
+
+impl From<BuildMoveError> for TestError {
+    fn from(value: BuildMoveError) -> Self {
+        TestError::BuildMove(value)
+    }
+}
diff --git a/moves/tests/flags.rs b/moves/tests/flags.rs
new file mode 100644
index 0000000..6d001cb
--- /dev/null
+++ b/moves/tests/flags.rs
@@ -0,0 +1,109 @@
+// Eryn Wells <eryn@erynwells.me>
+
+use chessfriend_core::{piece, Color, File, Shape, Square};
+use chessfriend_moves::{testing::*, Builder, Castle, PromotionShape};
+
+macro_rules! assert_flag {
+    ($move:expr, $left:expr, $right:expr, $desc:expr) => {
+        assert_eq!($left, $right, "{:?} -> {}", $move, stringify!($desc))
+    };
+}
+
+macro_rules! assert_flags {
+    ($move:expr, $quiet:expr, $double_push:expr, $en_passant:expr, $capture:expr, $castle:expr, $promotion:expr) => {
+        assert_flag!($move, $move.is_quiet(), $quiet, "is_quiet");
+        assert_flag!(
+            $move,
+            $move.is_double_push(),
+            $double_push,
+            "is_double_push"
+        );
+        assert_flag!($move, $move.is_en_passant(), $en_passant, "is_en_passant");
+        assert_flag!($move, $move.is_capture(), $capture, "is_capture");
+        assert_flag!($move, $move.is_castle(), $castle, "is_castle");
+        assert_flag!($move, $move.is_promotion(), $promotion, "is_promotion");
+    };
+}
+
+#[test]
+fn move_flags_quiet() -> TestResult {
+    let mv = Builder::push(&piece!(White Pawn on A4))
+        .to(Square::A5)
+        .build()?;
+    assert_flags!(mv, true, false, false, false, false, false);
+
+    Ok(())
+}
+
+#[test]
+fn move_flags_double_push() -> TestResult {
+    let mv = Builder::double_push(File::C, Color::White).build()?;
+    assert_flags!(mv, false, true, false, false, false, false);
+
+    Ok(())
+}
+
+#[test]
+fn move_flags_capture() -> TestResult {
+    let mv = Builder::new()
+        .from(Square::A4)
+        .capturing_on(Square::B5)
+        .build()?;
+
+    assert_flags!(mv, false, false, false, true, false, false);
+
+    Ok(())
+}
+
+#[test]
+fn move_flags_en_passant_capture() -> TestResult {
+    let mv = unsafe {
+        Builder::new()
+            .from(Square::A4)
+            .capturing_en_passant_on(Square::B3)
+            .build_unchecked()
+    };
+
+    assert_flags!(mv, false, false, true, true, false, false);
+    assert_eq!(mv.origin_square(), Square::A4);
+    assert_eq!(mv.target_square(), Square::B3);
+    assert_eq!(mv.capture_square(), Some(Square::B4));
+
+    Ok(())
+}
+
+#[test]
+fn move_flags_promotion() -> TestResult {
+    let mv = Builder::push(&piece!(White Pawn on H7))
+        .to(Square::H8)
+        .promoting_to(PromotionShape::Queen)
+        .build()?;
+
+    assert_flags!(mv, false, false, false, false, false, true);
+    assert_eq!(mv.promotion(), Some(Shape::Queen));
+
+    Ok(())
+}
+
+#[test]
+fn move_flags_capture_promotion() -> TestResult {
+    let mv = Builder::push(&piece!(White Pawn on H7))
+        .to(Square::H8)
+        .capturing_piece(&piece!(Black Knight on G8))
+        .promoting_to(PromotionShape::Queen)
+        .build()?;
+
+    assert_flags!(mv, false, false, false, true, false, true);
+    assert_eq!(mv.promotion(), Some(Shape::Queen));
+
+    Ok(())
+}
+
+#[test]
+fn move_flags_castle() -> TestResult {
+    let mv = Builder::castling(Color::White, Castle::KingSide).build()?;
+
+    assert_flags!(mv, false, false, false, false, true, false);
+
+    Ok(())
+}
diff --git a/moves/tests/pushes.rs b/moves/tests/pushes.rs
new file mode 100644
index 0000000..7406eb0
--- /dev/null
+++ b/moves/tests/pushes.rs
@@ -0,0 +1,17 @@
+// Eryn Wells <eryn@erynwells.me>
+
+use chessfriend_core::{piece, Square};
+use chessfriend_moves::{testing::*, Builder};
+
+#[test]
+fn pawn_push() -> TestResult {
+    let mv = Builder::push(&piece!(White Pawn on A3))
+        .to(Square::A4)
+        .build()?;
+
+    assert!(mv.is_quiet());
+    assert_eq!(mv.origin_square(), Square::A3);
+    assert_eq!(mv.target_square(), Square::A4);
+
+    Ok(())
+}
diff --git a/position/Cargo.toml b/position/Cargo.toml
index db11c0d..07157eb 100644
--- a/position/Cargo.toml
+++ b/position/Cargo.toml
@@ -8,3 +8,4 @@ edition = "2021"
 [dependencies]
 chessfriend_core = { path = "../core" }
 chessfriend_bitboard = { path = "../bitboard" }
+chessfriend_moves = { path = "../moves" }
diff --git a/position/src/check.rs b/position/src/check.rs
index 05e34b7..a3f2804 100644
--- a/position/src/check.rs
+++ b/position/src/check.rs
@@ -1,7 +1,7 @@
 // Eryn Wells <eryn@erynwells.me>
 
 use chessfriend_bitboard::BitBoard;
-use chessfriend_core::{Color, Direction, Shape, Square};
+use chessfriend_core::Shape;
 
 use crate::sight::SliderRayToSquareExt;
 
diff --git a/position/src/fen.rs b/position/src/fen.rs
index d6c3568..fde920c 100644
--- a/position/src/fen.rs
+++ b/position/src/fen.rs
@@ -1,9 +1,11 @@
 // Eryn Wells <eryn@erynwells.me>
 
-use crate::{r#move::Castle, Position, PositionBuilder};
+use crate::{Position, PositionBuilder};
 use chessfriend_core::{piece, Color, File, Piece, PlacedPiece, Rank, Square};
+use chessfriend_moves::{Castle, EnPassant};
 use std::fmt::Write;
 
+#[macro_export]
 macro_rules! fen {
     ($fen_string:literal) => {
         Position::from_fen_str($fen_string)
@@ -95,11 +97,8 @@ impl ToFen for Position {
         write!(
             fen_string,
             " {}",
-            if let Some(en_passant_square) = self.en_passant_square() {
-                en_passant_square.to_string()
-            } else {
-                "-".to_string()
-            }
+            self.en_passant()
+                .map_or("-".to_string(), |ep| ep.target_square().to_string())
         )
         .map_err(|err| ToFenError::FmtError(err))?;
 
@@ -197,7 +196,7 @@ impl FromFen for Position {
         let en_passant_square = fields.next().ok_or(FromFenError)?;
         if en_passant_square != "-" {
             let square = Square::from_algebraic_str(en_passant_square).map_err(|_| FromFenError)?;
-            builder.en_passant_square(Some(square));
+            builder.en_passant(Some(EnPassant::from_target_square(square).unwrap()));
         }
 
         let half_move_clock = fields.next().ok_or(FromFenError)?;
diff --git a/position/src/lib.rs b/position/src/lib.rs
index 5776e05..1995be0 100644
--- a/position/src/lib.rs
+++ b/position/src/lib.rs
@@ -4,7 +4,6 @@ pub mod fen;
 
 mod check;
 mod display;
-mod r#move;
 mod move_generator;
 mod position;
 mod sight;
@@ -12,8 +11,8 @@ mod sight;
 #[macro_use]
 mod macros;
 
+#[cfg(test)]
 #[macro_use]
-mod tests;
+mod testing;
 
-pub use position::{MoveBuilder as MakeMoveBuilder, Position, PositionBuilder};
-pub use r#move::{Castle, MakeMoveError, Move, MoveBuilder};
+pub use position::{MakeMoveError, MoveBuilder as MakeMoveBuilder, Position, PositionBuilder};
diff --git a/position/src/macros.rs b/position/src/macros.rs
index c7998d7..260a502 100644
--- a/position/src/macros.rs
+++ b/position/src/macros.rs
@@ -16,6 +16,7 @@ macro_rules! position {
     };
 }
 
+#[cfg(test)]
 #[macro_export]
 macro_rules! test_position {
     ($to_move:ident, [ $($color:ident $shape:ident on $square:ident),* $(,)? ], $en_passant:ident) => {
@@ -31,7 +32,7 @@ macro_rules! test_position {
                 ))
             )*
             .to_move(chessfriend_core::Color::$to_move)
-            .en_passant_square(Some(chessfriend_core::Square::$en_passant))
+            .en_passant(Some(chessfriend_moves::EnPassant::from_target_square(chessfriend_core::Square::$en_passant)).unwrap())
             .build();
             println!("{pos}");
 
diff --git a/position/src/move.rs b/position/src/move.rs
deleted file mode 100644
index 32bc399..0000000
--- a/position/src/move.rs
+++ /dev/null
@@ -1,602 +0,0 @@
-// Eryn Wells <eryn@erynwells.me>
-
-use chessfriend_core::{Piece, PlacedPiece, Rank, Shape, Square};
-use std::fmt;
-
-pub use castle::Castle;
-pub(crate) use move_formatter::AlgebraicMoveFormatter;
-
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
-pub enum MakeMoveError {
-    PlayerOutOfTurn,
-    NoPiece,
-    NoCapturedPiece,
-    NoLegalMoves,
-    IllegalCastle,
-    IllegalSquare(Square),
-}
-
-mod castle {
-    use chessfriend_bitboard::BitBoard;
-    use chessfriend_core::{Color, Square};
-
-    #[repr(u16)]
-    #[derive(Copy, Clone, Debug, Eq, PartialEq)]
-    pub enum Castle {
-        KingSide = 0b10,
-        QueenSide = 0b11,
-    }
-
-    pub(crate) struct CastlingParameters {
-        clear_squares: BitBoard,
-        check_squares: BitBoard,
-    }
-
-    #[derive(Debug)]
-    pub(crate) struct Squares {
-        pub king: Square,
-        pub rook: Square,
-    }
-
-    impl Castle {
-        pub const ALL: [Castle; 2] = [Castle::KingSide, Castle::QueenSide];
-
-        const STARTING_SQUARES: [[Squares; 2]; 2] = [
-            [
-                Squares {
-                    king: Square::E1,
-                    rook: Square::H1,
-                },
-                Squares {
-                    king: Square::E1,
-                    rook: Square::A1,
-                },
-            ],
-            [
-                Squares {
-                    king: Square::E8,
-                    rook: Square::H8,
-                },
-                Squares {
-                    king: Square::E8,
-                    rook: Square::A8,
-                },
-            ],
-        ];
-
-        const TARGET_SQUARES: [[Squares; 2]; 2] = [
-            [
-                Squares {
-                    king: Square::G1,
-                    rook: Square::F1,
-                },
-                Squares {
-                    king: Square::C1,
-                    rook: Square::D1,
-                },
-            ],
-            [
-                Squares {
-                    king: Square::G8,
-                    rook: Square::F8,
-                },
-                Squares {
-                    king: Square::C8,
-                    rook: Square::D8,
-                },
-            ],
-        ];
-
-        pub(crate) fn starting_squares(&self, color: Color) -> &'static Squares {
-            &Castle::STARTING_SQUARES[color as usize][self.into_index()]
-        }
-
-        pub(crate) fn target_squares(&self, color: Color) -> &'static Squares {
-            &Castle::TARGET_SQUARES[color as usize][self.into_index()]
-        }
-
-        pub(crate) fn into_index(&self) -> usize {
-            match self {
-                Castle::KingSide => 0,
-                Castle::QueenSide => 1,
-            }
-        }
-
-        pub(crate) fn parameters(&self) -> CastlingParameters {
-            match self {
-                Castle::KingSide => CastlingParameters {
-                    clear_squares: BitBoard::new(0b01100000),
-                    check_squares: BitBoard::new(0b01110000),
-                },
-                Castle::QueenSide => CastlingParameters {
-                    clear_squares: BitBoard::new(0b00001110),
-                    check_squares: BitBoard::new(0b00011100),
-                },
-            }
-        }
-    }
-
-    impl CastlingParameters {
-        pub fn clear_squares(&self) -> &BitBoard {
-            &self.clear_squares
-        }
-
-        pub fn check_squares(&self) -> &BitBoard {
-            &self.check_squares
-        }
-    }
-}
-
-#[repr(u16)]
-#[derive(Copy, Clone, Debug, Eq, PartialEq)]
-pub enum PromotableShape {
-    Knight = 0b00,
-    Bishop = 0b01,
-    Rook = 0b10,
-    Queen = 0b11,
-}
-
-impl TryFrom<Shape> for PromotableShape {
-    type Error = ();
-
-    fn try_from(value: Shape) -> Result<Self, Self::Error> {
-        match value {
-            Shape::Knight => Ok(PromotableShape::Knight),
-            Shape::Bishop => Ok(PromotableShape::Bishop),
-            Shape::Rook => Ok(PromotableShape::Rook),
-            Shape::Queen => Ok(PromotableShape::Queen),
-            _ => Err(()),
-        }
-    }
-}
-
-#[repr(u16)]
-#[derive(Copy, Clone, Debug, Eq, PartialEq)]
-enum Kind {
-    Quiet = 0b00,
-    DoublePush = 0b01,
-    Castle(Castle),
-    Capture(PlacedPiece) = 0b0100,
-    EnPassantCapture(PlacedPiece) = 0b0101,
-    Promotion(PromotableShape) = 0b1000,
-    CapturePromotion(PlacedPiece, PromotableShape) = 0b1100,
-}
-
-impl Kind {
-    fn bits(&self) -> u16 {
-        match self {
-            Self::Promotion(shape) => self.discriminant() | *shape as u16,
-            Self::CapturePromotion(_, shape) => self.discriminant() | *shape as u16,
-            Self::Castle(castle) => *castle as u16,
-            _ => self.discriminant(),
-        }
-    }
-
-    /// Return the discriminant value. This implementation is copied from the Rust docs.
-    /// See https://doc.rust-lang.org/std/mem/fn.discriminant.html
-    fn discriminant(&self) -> u16 {
-        unsafe { *<*const _>::from(self).cast::<u16>() }
-    }
-}
-
-impl Default for Kind {
-    fn default() -> Self {
-        Self::Quiet
-    }
-}
-
-/// A single player's move. In chess parlance, this is a "ply".
-#[derive(Clone, Copy, Eq, Hash, PartialEq)]
-pub struct Move(u16);
-
-impl Move {
-    pub fn from_square(&self) -> Square {
-        ((self.0 >> 4) & 0b111111).try_into().unwrap()
-    }
-
-    pub fn to_square(&self) -> Square {
-        (self.0 >> 10).try_into().unwrap()
-    }
-
-    pub fn is_quiet(&self) -> bool {
-        self.flags() == Kind::Quiet.discriminant()
-    }
-
-    pub fn is_double_push(&self) -> bool {
-        self.flags() == Kind::DoublePush.discriminant()
-    }
-
-    pub fn is_castle(&self) -> bool {
-        self.castle().is_some()
-    }
-
-    pub fn castle(&self) -> Option<Castle> {
-        match self.flags() {
-            0b0010 => Some(Castle::KingSide),
-            0b0011 => Some(Castle::QueenSide),
-            _ => None,
-        }
-    }
-
-    pub fn is_capture(&self) -> bool {
-        (self.0 & 0b0100) != 0
-    }
-
-    pub fn is_en_passant(&self) -> bool {
-        self.flags() == 0b0101
-    }
-
-    pub fn is_promotion(&self) -> bool {
-        (self.0 & 0b1000) != 0
-    }
-
-    pub fn promotion(&self) -> Option<Shape> {
-        if !self.is_promotion() {
-            return None;
-        }
-
-        Some(match self.special() {
-            0b00 => Shape::Knight,
-            0b01 => Shape::Bishop,
-            0b10 => Shape::Rook,
-            0b11 => Shape::Queen,
-            _ => unreachable!(),
-        })
-    }
-
-    #[inline]
-    fn flags(&self) -> u16 {
-        self.0 & 0b1111
-    }
-
-    #[inline]
-    fn special(&self) -> u16 {
-        self.0 & 0b11
-    }
-}
-
-impl fmt::Debug for Move {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_tuple("Move")
-            .field(&format_args!("{:08b}", &self.0))
-            .finish()
-    }
-}
-
-#[derive(Clone, Debug)]
-pub struct MoveBuilder {
-    piece: Piece,
-    from: Square,
-    to: Square,
-    kind: Kind,
-}
-
-impl MoveBuilder {
-    pub fn new(piece: Piece, from: Square, to: Square) -> Self {
-        let kind = match piece.shape() {
-            Shape::Pawn => {
-                let from_rank = from.rank();
-                let to_rank = to.rank();
-                let is_white_double_push = from_rank == Rank::TWO && to_rank == Rank::FOUR;
-                let is_black_double_push = from_rank == Rank::SEVEN && to_rank == Rank::FIVE;
-                if is_white_double_push || is_black_double_push {
-                    Kind::DoublePush
-                } else {
-                    Kind::Quiet
-                }
-            }
-            _ => Kind::Quiet,
-        };
-
-        Self {
-            piece,
-            from,
-            to,
-            kind,
-        }
-    }
-
-    pub fn castle(mut self, castle: Castle) -> Self {
-        self.kind = Kind::Castle(castle);
-        self
-    }
-
-    pub fn capturing(mut self, captured_piece: PlacedPiece) -> Self {
-        self.kind = match self.kind {
-            Kind::Promotion(shape) => Kind::CapturePromotion(captured_piece, shape),
-            _ => Kind::Capture(captured_piece),
-        };
-        self
-    }
-
-    pub fn capturing_en_passant(mut self, captured_piece: PlacedPiece) -> Self {
-        self.kind = Kind::EnPassantCapture(captured_piece);
-        self
-    }
-
-    pub fn promoting_to(mut self, shape: Shape) -> Self {
-        if let Some(shape) = PromotableShape::try_from(shape).ok() {
-            self.kind = match self.kind {
-                Kind::Capture(piece) => Kind::CapturePromotion(piece, shape),
-                Kind::CapturePromotion(piece, _) => Kind::CapturePromotion(piece, shape),
-                _ => Kind::Promotion(shape),
-            };
-        }
-        self
-    }
-
-    pub fn build(&self) -> Move {
-        Move(
-            self.kind.bits()
-                | ((self.from as u16 & 0b111111) << 4)
-                | ((self.to as u16 & 0b111111) << 10),
-        )
-    }
-}
-
-mod move_formatter {
-    use super::{Castle, Move};
-    use crate::Position;
-    use chessfriend_core::Shape;
-    use std::fmt;
-
-    enum Style {
-        Short,
-        Long,
-    }
-
-    impl Default for Style {
-        fn default() -> Self {
-            Style::Long
-        }
-    }
-
-    pub(crate) struct AlgebraicMoveFormatter<'m, 'pos> {
-        position: &'pos Position,
-        r#move: &'m Move,
-        style: Style,
-    }
-
-    impl<'pos, 'm> AlgebraicMoveFormatter<'m, 'pos> {
-        pub(crate) fn new(
-            mv: &'m Move,
-            position: &'pos Position,
-        ) -> AlgebraicMoveFormatter<'m, 'pos> {
-            AlgebraicMoveFormatter {
-                position,
-                r#move: mv,
-                style: Style::default(),
-            }
-        }
-
-        fn style(mut self, style: Style) -> Self {
-            self.style = style;
-            self
-        }
-
-        fn fmt_kingside_castle(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-            write!(f, "0-0")
-        }
-
-        fn fmt_queenside_castle(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-            write!(f, "0-0-0")
-        }
-
-        fn fmt_short(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-            unimplemented!()
-        }
-
-        fn fmt_long(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-            // TODO: Figure out how to write the short algebraic form, where a
-            // disambiguating coordiate is specified when two of the same piece
-            // cam move to the same square.
-
-            // TODO: Write better pawn moves.
-
-            let mv = self.r#move;
-            let from_square = mv.from_square();
-            let to_square = mv.to_square();
-
-            let piece = self
-                .position
-                .piece_on_square(from_square)
-                .expect(&format!("No piece on {}", from_square));
-            if piece.shape() != Shape::Pawn {
-                write!(f, "{}", piece.shape())?;
-            }
-
-            write!(
-                f,
-                "{}{}{}",
-                from_square,
-                if mv.is_capture() { 'x' } else { '-' },
-                to_square,
-            )?;
-
-            if let Some(promotion) = mv.promotion() {
-                write!(f, "={}", promotion)?;
-            }
-
-            // TODO: Write check (+) and checkmate (#) symbols
-
-            Ok(())
-        }
-    }
-
-    impl<'pos, 'mv> fmt::Display for AlgebraicMoveFormatter<'mv, 'pos> {
-        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-            let mv = self.r#move;
-            match mv.castle() {
-                Some(Castle::KingSide) => return self.fmt_kingside_castle(f),
-                Some(Castle::QueenSide) => return self.fmt_queenside_castle(f),
-                _ => {}
-            }
-
-            match self.style {
-                Style::Short => self.fmt_short(f),
-                Style::Long => self.fmt_long(f),
-            }
-        }
-    }
-
-    #[cfg(test)]
-    mod tests {
-        use super::{AlgebraicMoveFormatter, Style};
-        use crate::position;
-        use chessfriend_core::piece;
-
-        macro_rules! chess_move {
-            ($color:ident $shape:ident $from_square:ident - $to_square:ident) => {
-                $crate::MoveBuilder::new(
-                    chessfriend_core::Piece::new(
-                        chessfriend_core::Color::$color,
-                        chessfriend_core::Shape::$shape,
-                    ),
-                    chessfriend_core::Square::$from_square,
-                    chessfriend_core::Square::$to_square,
-                )
-                .build()
-            };
-            ($color:ident $shape:ident $from_square:ident x $to_square:ident, $captured_color:ident $captured_shape:ident) => {
-                $crate::MoveBuilder::new(
-                    chessfriend_core::Piece::new(
-                        chessfriend_core::Color::$color,
-                        chessfriend_core::Shape::$shape,
-                    ),
-                    chessfriend_core::Square::$from_square,
-                    chessfriend_core::Square::$to_square,
-                )
-                .capturing(chessfriend_core::PlacedPiece::new(
-                    chessfriend_core::Piece::new(
-                        chessfriend_core::Color::$captured_color,
-                        chessfriend_core::Shape::$captured_shape,
-                    ),
-                    chessfriend_core::Square::$to_square,
-                ))
-                .build()
-            };
-        }
-
-        macro_rules! test_algebraic_formatter {
-            ($test_name:ident, $style:ident, $color:ident $shape:ident $from_square:ident x $to_square:ident, $captured_color:ident $captured_shape:ident, $output:expr) => {
-                #[test]
-                fn $test_name() {
-                    let pos = position![
-                        $color $shape on $from_square,
-                        $captured_color $captured_shape on $to_square,
-                    ];
-                    let mv = chess_move!(
-                        $color $shape $from_square x $to_square,
-                        $captured_color $captured_shape
-                    );
-
-                    println!("{:?}", &mv);
-
-                    let formatter = AlgebraicMoveFormatter::new(&mv, &pos).style(Style::$style);
-                    assert_eq!(format!("{}", formatter), $output);
-                }
-            };
-            ($test_name:ident, $style:ident, $color:ident $shape:ident $from_square:ident - $to_square:ident, $output:expr) => {
-                #[test]
-                fn $test_name() {
-                    let pos = position![
-                        $color $shape on $from_square,
-                    ];
-
-                    let mv = chess_move!($color $shape $from_square-$to_square);
-                    println!("{:?}", &mv);
-
-                    let formatter = AlgebraicMoveFormatter::new(&mv, &pos).style(Style::$style);
-                    assert_eq!(format!("{}", formatter), $output);
-                }
-            };
-        }
-
-        test_algebraic_formatter!(long_pawn_move, Long, White Pawn E4 - E5, "e4-e5");
-        test_algebraic_formatter!(long_bishop_move, Long, White Bishop A4 - D7, "Ba4-d7");
-        test_algebraic_formatter!(long_bishop_capture, Long, White Bishop A2 x E6, Black Knight, "Ba2xe6");
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use chessfriend_core::piece;
-
-    macro_rules! assert_flag {
-        ($move:expr, $left:expr, $right:expr, $desc:expr) => {
-            assert_eq!($left, $right, "{:?} -> {}", $move, stringify!($desc))
-        };
-    }
-
-    macro_rules! assert_flags {
-        ($move:expr, $quiet:expr, $double_push:expr, $en_passant:expr, $capture:expr, $castle:expr, $promotion:expr) => {
-            assert_flag!($move, $move.is_quiet(), $quiet, "is_quiet");
-            assert_flag!(
-                $move,
-                $move.is_double_push(),
-                $double_push,
-                "is_double_push"
-            );
-            assert_flag!($move, $move.is_en_passant(), $en_passant, "is_en_passant");
-            assert_flag!($move, $move.is_capture(), $capture, "is_capture");
-            assert_flag!($move, $move.is_castle(), $castle, "is_castle");
-            assert_flag!($move, $move.is_promotion(), $promotion, "is_promotion");
-        };
-    }
-
-    #[test]
-    fn move_flags_quiet() {
-        let mv = MoveBuilder::new(piece!(White Pawn), Square::A4, Square::A5).build();
-        assert_flags!(mv, true, false, false, false, false, false);
-    }
-
-    #[test]
-    fn move_flags_double_push() {
-        let mv = MoveBuilder::new(piece!(White Pawn), Square::C2, Square::C4).build();
-        assert_flags!(mv, false, true, false, false, false, false);
-    }
-
-    #[test]
-    fn move_flags_capture() {
-        let mv = MoveBuilder::new(piece!(White Pawn), Square::A4, Square::B5)
-            .capturing(piece!(Black Bishop on B5))
-            .build();
-        assert_flags!(mv, false, false, false, true, false, false);
-    }
-
-    #[test]
-    fn move_flags_en_passant_capture() {
-        let mv = MoveBuilder::new(piece!(White Pawn), Square::A5, Square::B6)
-            .capturing_en_passant(piece!(Black Pawn on B5))
-            .build();
-        assert_flags!(mv, false, false, true, true, false, false);
-    }
-
-    #[test]
-    fn move_flags_promotion() {
-        let mv = MoveBuilder::new(piece!(White Pawn), Square::H7, Square::H8)
-            .promoting_to(Shape::Queen)
-            .build();
-        assert_flags!(mv, false, false, false, false, false, true);
-        assert_eq!(mv.promotion(), Some(Shape::Queen));
-    }
-
-    #[test]
-    fn move_flags_capture_promotion() {
-        let mv = MoveBuilder::new(piece!(White Pawn), Square::H7, Square::G8)
-            .capturing(piece!(Black Knight on G8))
-            .promoting_to(Shape::Queen)
-            .build();
-        assert_flags!(mv, false, false, false, true, false, true);
-        assert_eq!(mv.promotion(), Some(Shape::Queen));
-    }
-
-    #[test]
-    fn move_flags_castle() {
-        let mv = MoveBuilder::new(piece!(Black King), Square::E8, Square::G8)
-            .castle(Castle::KingSide)
-            .build();
-        assert_flags!(mv, false, false, false, false, true, false);
-    }
-}
diff --git a/position/src/move_generator.rs b/position/src/move_generator.rs
index e6884d4..c4271ce 100644
--- a/position/src/move_generator.rs
+++ b/position/src/move_generator.rs
@@ -7,6 +7,8 @@ mod move_set;
 mod pawn;
 mod queen;
 mod rook;
+
+#[cfg(test)]
 mod tests;
 
 pub(crate) use move_set::MoveSet;
@@ -17,9 +19,10 @@ use self::{
     queen::ClassicalMoveGenerator as QueenMoveGenerator,
     rook::ClassicalMoveGenerator as RookMoveGenerator,
 };
-use crate::{Move, Position};
+use crate::Position;
 use chessfriend_bitboard::BitBoard;
 use chessfriend_core::{Color, Piece, PlacedPiece, Shape, Square};
+use chessfriend_moves::Move;
 use std::collections::BTreeMap;
 
 trait MoveGenerator {
@@ -53,7 +56,7 @@ macro_rules! move_generator_declaration {
                 push_mask: chessfriend_bitboard::BitBoard,
             ) -> $name {
                 let move_sets = if Self::shape() == chessfriend_core::Shape::King
-                    || (!capture_mask.is_empty() && !push_mask.is_empty())
+                    || !(capture_mask.is_empty() && push_mask.is_empty())
                 {
                     Self::move_sets(position, color, capture_mask, push_mask)
                 } else {
@@ -66,7 +69,7 @@ macro_rules! move_generator_declaration {
     };
     ($name:ident, getters) => {
         impl $name {
-            pub(super) fn iter(&self) -> impl Iterator<Item = $crate::Move> + '_ {
+            pub(super) fn iter(&self) -> impl Iterator<Item = chessfriend_moves::Move> + '_ {
                 self.move_sets.values().flat_map(|set| set.moves())
             }
 
@@ -77,7 +80,8 @@ macro_rules! move_generator_declaration {
                 self.move_sets.get(&piece.square())
             }
 
-            fn bitboard(&self) -> chessfriend_bitboard::BitBoard {
+            #[cfg(test)]
+            fn _test_bitboard(&self) -> chessfriend_bitboard::BitBoard {
                 self.move_sets.values().fold(
                     chessfriend_bitboard::BitBoard::empty(),
                     |partial, mv_set| partial | mv_set.bitboard(),
diff --git a/position/src/move_generator/bishop.rs b/position/src/move_generator/bishop.rs
index 5630246..a57b1a4 100644
--- a/position/src/move_generator/bishop.rs
+++ b/position/src/move_generator/bishop.rs
@@ -72,7 +72,7 @@ mod tests {
             ClassicalMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
         assert_eq!(
-            generator.bitboard(),
+            generator._test_bitboard(),
             BitBoard::new(
                 0b10000000_01000000_00100000_00010000_00001000_00000100_00000010_00000000
             )
@@ -93,7 +93,7 @@ mod tests {
             ClassicalMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
         assert_eq!(
-            generator.bitboard(),
+            generator._test_bitboard(),
             BitBoard::new(
                 0b00000000_00000000_00000000_00000000_00001000_00000100_00000010_00000000
             )
@@ -112,7 +112,7 @@ mod tests {
             ClassicalMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
         assert_eq!(
-            generator.bitboard(),
+            generator._test_bitboard(),
             BitBoard::new(
                 0b00000000_00000000_00000000_00000000_00000000_00000100_00000010_00000000
             )
@@ -129,7 +129,7 @@ mod tests {
 
         let generator =
             ClassicalMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
-        let bitboard = generator.bitboard();
+        let bitboard = generator._test_bitboard();
         let expected = BitBoard::new(
             0b00000001_10000010_01000100_00101000_00000000_00101000_01000100_10000010,
         );
diff --git a/position/src/move_generator/king.rs b/position/src/move_generator/king.rs
index befd0b2..3443d46 100644
--- a/position/src/move_generator/king.rs
+++ b/position/src/move_generator/king.rs
@@ -4,9 +4,10 @@
 //! generating the possible moves for the king in the given position.
 
 use super::{move_generator_declaration, MoveGeneratorInternal, MoveSet};
-use crate::{r#move::Castle, Position};
+use crate::Position;
 use chessfriend_bitboard::BitBoard;
 use chessfriend_core::{PlacedPiece, Shape};
+use chessfriend_moves::Castle;
 
 move_generator_declaration!(KingMoveGenerator, struct);
 move_generator_declaration!(KingMoveGenerator, new);
@@ -57,59 +58,64 @@ impl MoveGeneratorInternal for KingMoveGenerator {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::{assert_move_list, position, test_position, Move, MoveBuilder, PositionBuilder};
+    use crate::{assert_move_list, position, test_position, testing::*, PositionBuilder};
     use chessfriend_bitboard::bitboard;
     use chessfriend_core::{piece, Color, Square};
+    use chessfriend_moves::{Builder as MoveBuilder, Castle, Move};
     use std::collections::HashSet;
 
     #[test]
-    fn one_king() {
+    fn one_king() -> TestResult {
         let pos = position![White King on E4];
 
         let generator = KingMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
         assert_eq!(
-            generator.bitboard(),
+            generator._test_bitboard(),
             bitboard![E5, F5, F4, F3, E3, D3, D4, D5]
         );
 
+        let builder = MoveBuilder::push(&piece!(White King on E4));
         let expected_moves: HashSet<Move> = HashSet::from_iter([
-            MoveBuilder::new(piece!(White King), Square::E4, Square::D5).build(),
-            MoveBuilder::new(piece!(White King), Square::E4, Square::E5).build(),
-            MoveBuilder::new(piece!(White King), Square::E4, Square::F5).build(),
-            MoveBuilder::new(piece!(White King), Square::E4, Square::F4).build(),
-            MoveBuilder::new(piece!(White King), Square::E4, Square::F3).build(),
-            MoveBuilder::new(piece!(White King), Square::E4, Square::E3).build(),
-            MoveBuilder::new(piece!(White King), Square::E4, Square::D3).build(),
-            MoveBuilder::new(piece!(White King), Square::E4, Square::D4).build(),
+            builder.clone().to(Square::D5).build()?,
+            builder.clone().to(Square::E5).build()?,
+            builder.clone().to(Square::F5).build()?,
+            builder.clone().to(Square::F4).build()?,
+            builder.clone().to(Square::F3).build()?,
+            builder.clone().to(Square::E3).build()?,
+            builder.clone().to(Square::D3).build()?,
+            builder.clone().to(Square::D4).build()?,
         ]);
 
         let generated_moves: HashSet<Move> = generator.iter().collect();
 
         assert_move_list!(generated_moves, expected_moves, pos);
+
+        Ok(())
     }
 
     #[test]
-    fn one_king_corner() {
+    fn one_king_corner() -> TestResult {
         let pos = position![White King on A1];
 
         let generator = KingMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
-        let generated_bitboard = generator.bitboard();
+        let generated_bitboard = generator._test_bitboard();
         let expected_bitboard = bitboard![A2, B2, B1];
         assert_eq!(
-            generator.bitboard(),
+            generator._test_bitboard(),
             bitboard![A2, B2, B1],
             "Generated:\n{generated_bitboard}\nExpected:\n{expected_bitboard}"
         );
 
+        let builder = MoveBuilder::push(&piece!(White King on A1));
         let expected_moves = [
-            MoveBuilder::new(piece!(White King), Square::A1, Square::A2).build(),
-            MoveBuilder::new(piece!(White King), Square::A1, Square::B1).build(),
-            MoveBuilder::new(piece!(White King), Square::A1, Square::B2).build(),
+            builder.clone().to(Square::A2).build()?,
+            builder.clone().to(Square::B1).build()?,
+            builder.clone().to(Square::B2).build()?,
         ];
 
-        let mut generated_moves: HashSet<Move> = generator.iter().collect();
+        let mut generated_moves: HashSet<_> = generator.iter().collect();
 
         for ex_move in expected_moves {
             assert!(
@@ -124,6 +130,8 @@ mod tests {
             "Moves unexpectedly present: {:#?}",
             generated_moves
         );
+
+        Ok(())
     }
 
     #[test]
@@ -138,7 +146,7 @@ mod tests {
         assert!(pos.is_king_in_check());
 
         let generator = KingMoveGenerator::new(&pos, Color::Black, BitBoard::FULL, BitBoard::FULL);
-        let generated_moves = generator.bitboard();
+        let generated_moves = generator._test_bitboard();
 
         let expected_moves = bitboard![F8, F7, F6, D6, D7, D8];
 
@@ -146,7 +154,7 @@ mod tests {
     }
 
     #[test]
-    fn white_king_unobstructed_castles() {
+    fn white_king_unobstructed_castles() -> TestResult {
         let pos = test_position!(
             White King on E1,
             White Rook on A1,
@@ -159,21 +167,16 @@ mod tests {
         let generator = KingMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
         let generated_moves: HashSet<Move> = generator.iter().collect();
 
-        let king = piece!(White King);
-        assert!(generated_moves.contains(
-            &MoveBuilder::new(king, Square::E1, Square::G1)
-                .castle(Castle::KingSide)
-                .build()
-        ));
-        assert!(generated_moves.contains(
-            &MoveBuilder::new(king, Square::E1, Square::C1)
-                .castle(Castle::QueenSide)
-                .build()
-        ));
+        assert!(generated_moves
+            .contains(&MoveBuilder::castling(Color::White, Castle::KingSide).build()?));
+        assert!(generated_moves
+            .contains(&MoveBuilder::castling(Color::White, Castle::QueenSide).build()?));
+
+        Ok(())
     }
 
     #[test]
-    fn white_king_obstructed_queenside_castle() {
+    fn white_king_obstructed_queenside_castle() -> TestResult {
         let pos = test_position!(
             White King on E1,
             White Knight on B1,
@@ -187,21 +190,16 @@ mod tests {
         let generator = KingMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
         let generated_moves: HashSet<Move> = generator.iter().collect();
 
-        let king = piece!(White King);
-        assert!(generated_moves.contains(
-            &MoveBuilder::new(king, Square::E1, Square::G1)
-                .castle(Castle::KingSide)
-                .build()
-        ));
-        assert!(!generated_moves.contains(
-            &MoveBuilder::new(king, Square::E1, Square::C1)
-                .castle(Castle::QueenSide)
-                .build()
-        ));
+        assert!(generated_moves
+            .contains(&MoveBuilder::castling(Color::White, Castle::KingSide).build()?));
+        assert!(!generated_moves
+            .contains(&MoveBuilder::castling(Color::White, Castle::QueenSide).build()?));
+
+        Ok(())
     }
 
     #[test]
-    fn white_king_obstructed_kingside_castle() {
+    fn white_king_obstructed_kingside_castle() -> TestResult {
         let pos = test_position!(
             White King on E1,
             White Rook on A1,
@@ -215,16 +213,11 @@ mod tests {
         let generator = KingMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
         let generated_moves: HashSet<Move> = generator.iter().collect();
 
-        let king = piece!(White King);
-        assert!(!generated_moves.contains(
-            &MoveBuilder::new(king, Square::E1, Square::G1)
-                .castle(Castle::KingSide)
-                .build()
-        ));
-        assert!(generated_moves.contains(
-            &MoveBuilder::new(king, Square::E1, Square::C1)
-                .castle(Castle::QueenSide)
-                .build()
-        ));
+        assert!(!generated_moves
+            .contains(&MoveBuilder::castling(Color::White, Castle::KingSide).build()?));
+        assert!(generated_moves
+            .contains(&MoveBuilder::castling(Color::White, Castle::QueenSide).build()?));
+
+        Ok(())
     }
 }
diff --git a/position/src/move_generator/knight.rs b/position/src/move_generator/knight.rs
index 6366808..2b385ec 100644
--- a/position/src/move_generator/knight.rs
+++ b/position/src/move_generator/knight.rs
@@ -34,54 +34,35 @@ impl MoveGeneratorInternal for KnightMoveGenerator {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::{position, Move, MoveBuilder};
+    use crate::{assert_move_list, position, testing::*};
     use chessfriend_core::{piece, Color, Square};
+    use chessfriend_moves::Builder as MoveBuilder;
     use std::collections::HashSet;
 
     #[test]
-    fn one_knight() {
+    fn one_knight() -> TestResult {
         let pos = position![
             White Knight on E4,
         ];
 
         let generator =
             KnightMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
+        let generated_moves: HashSet<_> = generator.iter().collect();
 
-        /*
-        let bb = generator.bitboard();
-        assert_eq!(
-            bb,
-            BitBoard::new(
-                0b00000000_00000000_00000000_00111000_00101000_00111000_00000000_00000000
-            )
-        );
-        */
+        let piece = piece!(White Knight on E4);
+        let expected_moves = HashSet::from_iter([
+            MoveBuilder::push(&piece).to(Square::C3).build()?,
+            MoveBuilder::push(&piece).to(Square::D2).build()?,
+            MoveBuilder::push(&piece).to(Square::F2).build()?,
+            MoveBuilder::push(&piece).to(Square::G3).build()?,
+            MoveBuilder::push(&piece).to(Square::C5).build()?,
+            MoveBuilder::push(&piece).to(Square::D6).build()?,
+            MoveBuilder::push(&piece).to(Square::G5).build()?,
+            MoveBuilder::push(&piece).to(Square::F6).build()?,
+        ]);
 
-        let expected_moves = [
-            MoveBuilder::new(piece!(White Knight), Square::E4, Square::C3).build(),
-            MoveBuilder::new(piece!(White Knight), Square::E4, Square::D2).build(),
-            MoveBuilder::new(piece!(White Knight), Square::E4, Square::F2).build(),
-            MoveBuilder::new(piece!(White Knight), Square::E4, Square::G3).build(),
-            MoveBuilder::new(piece!(White Knight), Square::E4, Square::C5).build(),
-            MoveBuilder::new(piece!(White Knight), Square::E4, Square::D6).build(),
-            MoveBuilder::new(piece!(White Knight), Square::E4, Square::G5).build(),
-            MoveBuilder::new(piece!(White Knight), Square::E4, Square::F6).build(),
-        ];
+        assert_move_list!(generated_moves, expected_moves, pos);
 
-        let mut generated_moves: HashSet<Move> = generator.iter().collect();
-
-        for ex_move in expected_moves {
-            assert!(
-                generated_moves.remove(&ex_move),
-                "{:#?} was not generated",
-                &ex_move
-            );
-        }
-
-        assert!(
-            generated_moves.is_empty(),
-            "Moves unexpectedly present: {:#?}",
-            generated_moves
-        );
+        Ok(())
     }
 }
diff --git a/position/src/move_generator/move_set.rs b/position/src/move_generator/move_set.rs
index 6cefb7a..61adb03 100644
--- a/position/src/move_generator/move_set.rs
+++ b/position/src/move_generator/move_set.rs
@@ -1,8 +1,8 @@
 // Eryn Wells <eryn@erynwells.me>
 
-use crate::{r#move::Castle, Move, MoveBuilder};
 use chessfriend_bitboard::BitBoard;
-use chessfriend_core::{Color, Piece, PlacedPiece, Shape, Square};
+use chessfriend_core::{PlacedPiece, Square};
+use chessfriend_moves::{Builder as MoveBuilder, Castle, EnPassant, Move};
 
 /// A set of bitboards defining the moves for a single piece on the board.
 #[derive(Clone, Debug, Default, Eq, PartialEq)]
@@ -11,12 +11,18 @@ struct BitBoardSet {
     captures: BitBoard,
 }
 
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub(crate) enum Special {
+    Pawn { en_passant: EnPassant },
+    King { castles: u8 },
+}
+
 /// A set of moves for a single piece on the board.
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub(crate) struct MoveSet {
     piece: PlacedPiece,
     bitboards: BitBoardSet,
-    special: u8,
+    special: Option<Special>,
 }
 
 impl MoveSet {
@@ -24,21 +30,53 @@ impl MoveSet {
         MoveSet {
             piece,
             bitboards: BitBoardSet::default(),
-            special: 0,
+            special: None,
         }
     }
 
-    pub(crate) fn can_move_to_square(&self, to: Square) -> bool {
-        self.bitboard().is_set(to)
+    pub(crate) fn can_move_to_square(&self, target_square: Square) -> bool {
+        match self.special {
+            Some(Special::King { castles }) => {
+                if self.check_castle_field(castles, Castle::KingSide)
+                    && target_square
+                        == Castle::KingSide
+                            .parameters(self.piece.color())
+                            .king_target_square()
+                {
+                    return true;
+                }
+
+                if self.check_castle_field(castles, Castle::KingSide)
+                    && target_square
+                        == Castle::QueenSide
+                            .parameters(self.piece.color())
+                            .king_target_square()
+                {
+                    return true;
+                }
+            }
+            Some(Special::Pawn { en_passant }) => {
+                if target_square == en_passant.target_square() {
+                    return true;
+                }
+            }
+            None => {}
+        }
+
+        self.bitboard().is_set(target_square)
     }
 
     pub(crate) fn can_castle(&self, castle: Castle) -> bool {
-        match castle {
-            Castle::KingSide => (self.special & 0b1) != 0,
-            Castle::QueenSide => (self.special & 0b10) != 0,
+        match self.special {
+            Some(Special::King { castles }) => self.check_castle_field(castles, castle),
+            _ => false,
         }
     }
 
+    fn check_castle_field(&self, castle_field: u8, castle: Castle) -> bool {
+        (castle_field & 1 << castle as u8) != 0
+    }
+
     pub(super) fn quiet_moves(mut self, bitboard: BitBoard) -> MoveSet {
         self.bitboards.quiet = bitboard;
         self
@@ -50,72 +88,103 @@ impl MoveSet {
     }
 
     pub(super) fn kingside_castle(&mut self) -> &mut MoveSet {
-        self.special |= 0b1;
+        match self.special {
+            Some(Special::King { ref mut castles }) => *castles |= 1 << Castle::KingSide as u8,
+            _ => {
+                self.special = Some(Special::King {
+                    castles: 1 << Castle::KingSide as u8,
+                })
+            }
+        }
+
         self
     }
 
     pub(super) fn queenside_castle(&mut self) -> &mut MoveSet {
-        self.special |= 0b10;
+        match self.special {
+            Some(Special::King { ref mut castles }) => *castles |= 1 << Castle::QueenSide as u8,
+            _ => {
+                self.special = Some(Special::King {
+                    castles: 1 << Castle::QueenSide as u8,
+                })
+            }
+        }
+
         self
     }
 
-    /// Return a BitBoard representing all possible moves.
+    pub(super) fn en_passant(&mut self, en_passant: EnPassant) -> &mut MoveSet {
+        self.special = Some(Special::Pawn { en_passant });
+        self
+    }
+
+    /// A `BitBoard` representing all possible moves.
     pub(super) fn bitboard(&self) -> BitBoard {
         self.bitboards.captures | self.bitboards.quiet
     }
 
     pub(crate) fn moves(&self) -> impl Iterator<Item = Move> + '_ {
-        let piece = self.piece.piece();
-        let from_square = self.piece.square();
+        let piece = &self.piece;
+        let color = piece.color();
+
+        let is_pawn_on_starting_rank =
+            piece.is_pawn() && piece.square().rank().is_pawn_starting_rank(color);
 
         self.bitboards
             .quiet
             .occupied_squares()
-            .map(move |to_square| MoveBuilder::new(*piece, from_square, to_square).build())
+            .filter_map(move |to_square| {
+                if is_pawn_on_starting_rank
+                    && to_square.rank().is_pawn_double_push_target_rank(color)
+                {
+                    MoveBuilder::double_push(piece.square().file(), color)
+                        .build()
+                        .ok()
+                } else {
+                    MoveBuilder::push(piece).to(to_square).build().ok()
+                }
+            })
             .chain(
                 self.bitboards
                     .captures
                     .occupied_squares()
-                    .map(move |to_square| {
-                        MoveBuilder::new(*piece, from_square, to_square)
-                            .capturing(PlacedPiece::new(
-                                Piece::new(Color::White, Shape::Pawn),
-                                to_square,
-                            ))
+                    .filter_map(|to_square| {
+                        MoveBuilder::push(piece)
+                            .capturing_on(to_square)
                             .build()
+                            .ok()
                     }),
             )
-            .chain(
-                if (self.special & 0b1) != 0 {
-                    Some(())
+            .chain(self.castle_move(Castle::KingSide))
+            .chain(self.castle_move(Castle::QueenSide))
+            .chain(self.en_passant_move())
+    }
+
+    fn castle_move(&self, castle: Castle) -> Option<Move> {
+        match self.special {
+            Some(Special::King { castles }) => {
+                if (castles & 1 << castle as u8) != 0 {
+                    Some(
+                        MoveBuilder::castling(self.piece.color(), castle)
+                            .build()
+                            .ok()?,
+                    )
                 } else {
                     None
                 }
-                .map(|()| {
-                    MoveBuilder::new(
-                        *piece,
-                        from_square,
-                        Castle::KingSide.target_squares(piece.color()).king,
-                    )
-                    .castle(Castle::KingSide)
-                    .build()
-                }),
-            )
-            .chain(
-                if (self.special & 0b10) != 0 {
-                    Some(())
-                } else {
-                    None
-                }
-                .map(|()| {
-                    MoveBuilder::new(
-                        *piece,
-                        from_square,
-                        Castle::QueenSide.target_squares(piece.color()).king,
-                    )
-                    .castle(Castle::QueenSide)
-                    .build()
-                }),
-            )
+            }
+            _ => None,
+        }
+    }
+
+    fn en_passant_move(&self) -> Option<Move> {
+        match self.special {
+            Some(Special::Pawn { en_passant }) => Some(unsafe {
+                MoveBuilder::push(&self.piece)
+                    .capturing_en_passant_on(en_passant.target_square())
+                    .build_unchecked()
+            }),
+            _ => None,
+        }
     }
 }
diff --git a/position/src/move_generator/pawn.rs b/position/src/move_generator/pawn.rs
index c6e7a5a..1a07c4c 100644
--- a/position/src/move_generator/pawn.rs
+++ b/position/src/move_generator/pawn.rs
@@ -4,11 +4,20 @@ use super::{move_generator_declaration, MoveGeneratorInternal, MoveSet};
 use crate::Position;
 use chessfriend_bitboard::BitBoard;
 use chessfriend_core::{Color, PlacedPiece, Rank, Shape, Square};
+use chessfriend_moves::{EnPassant, Move};
+use std::collections::BTreeMap;
 
 #[derive(Debug)]
 struct MoveIterator(usize, usize);
 
-move_generator_declaration!(PawnMoveGenerator);
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub(super) struct PawnMoveGenerator {
+    color: chessfriend_core::Color,
+    move_sets: BTreeMap<Square, MoveSet>,
+    en_passant_captures: Vec<Move>,
+}
+
+move_generator_declaration!(PawnMoveGenerator, getters);
 
 impl MoveGeneratorInternal for PawnMoveGenerator {
     fn shape() -> Shape {
@@ -24,14 +33,61 @@ impl MoveGeneratorInternal for PawnMoveGenerator {
         let capture_moves = Self::attacks(position, &placed_piece) & capture_mask;
         let quiet_moves = Self::pushes(position, &placed_piece) & push_mask;
 
-        MoveSet::new(*placed_piece)
+        let mut move_set = MoveSet::new(*placed_piece)
             .quiet_moves(quiet_moves)
-            .capture_moves(capture_moves)
+            .capture_moves(capture_moves);
+
+        if let Some(en_passant) =
+            Self::en_passant(position, placed_piece, &push_mask, &capture_mask)
+        {
+            move_set.en_passant(en_passant);
+        }
+
+        move_set
     }
 }
 
 impl PawnMoveGenerator {
-    fn pushes(position: &Position, piece: PlacedPiece) -> BitBoard {
+    pub(super) fn new(
+        position: &Position,
+        player_to_move: Color,
+        capture_mask: BitBoard,
+        push_mask: BitBoard,
+    ) -> Self {
+        let move_sets = if !(capture_mask.is_empty() && push_mask.is_empty()) {
+            Self::move_sets(position, player_to_move, capture_mask, push_mask)
+        } else {
+            std::collections::BTreeMap::new()
+        };
+
+        Self {
+            color: player_to_move,
+            move_sets,
+            en_passant_captures: Vec::new(),
+        }
+    }
+
+    fn move_sets(
+        position: &Position,
+        color: Color,
+        capture_mask: BitBoard,
+        push_mask: BitBoard,
+    ) -> BTreeMap<Square, MoveSet> {
+        let piece = Self::piece(color);
+        let moves_for_pieces =
+            BTreeMap::from_iter(position.bitboard_for_piece(piece).occupied_squares().map(
+                |square| {
+                    let piece = PlacedPiece::new(piece, square);
+                    let move_set =
+                        Self::move_set_for_piece(position, &piece, capture_mask, push_mask);
+                    (square, move_set)
+                },
+            ));
+
+        moves_for_pieces
+    }
+
+    fn pushes(position: &Position, piece: &PlacedPiece) -> BitBoard {
         let color = piece.color();
         let square = piece.square();
         let bitboard: BitBoard = square.into();
@@ -59,62 +115,109 @@ impl PawnMoveGenerator {
         }
     }
 
-    fn attacks(position: &Position, piece: PlacedPiece) -> BitBoard {
+    fn attacks(position: &Position, piece: &PlacedPiece) -> BitBoard {
         let color = piece.color();
 
         let opponent_pieces = position.bitboard_for_color(color.other());
-        let en_passant_bitboard = match position.en_passant_square() {
-            Some(square) => <Square as Into<BitBoard>>::into(square),
-            None => BitBoard::empty(),
-        };
 
-        BitBoard::pawn_attacks(piece.square(), color) & (opponent_pieces | en_passant_bitboard)
+        BitBoard::pawn_attacks(piece.square(), color) & opponent_pieces
+    }
+
+    fn en_passant(
+        position: &Position,
+        piece: &PlacedPiece,
+        push_mask: &BitBoard,
+        capture_mask: &BitBoard,
+    ) -> Option<EnPassant> {
+        match position.en_passant() {
+            Some(en_passant) => {
+                let target_square: BitBoard = en_passant.target_square().into();
+                let capture_square: BitBoard = en_passant.capture_square().into();
+
+                if (target_square & push_mask).is_empty()
+                    && (capture_square & capture_mask).is_empty()
+                {
+                    // Do not allow en passant if capturing would not either
+                    // block an active check, or capture a checking pawn.
+                    return None;
+                }
+
+                let capture = BitBoard::pawn_attacks(piece.square(), piece.color()) & target_square;
+                if capture.is_empty() {
+                    return None;
+                }
+
+                match position.piece_on_square(en_passant.capture_square()) {
+                    Some(_) => Some(en_passant),
+                    None => None,
+                }
+            }
+            None => None,
+        }
+    }
+
+    #[cfg(none)]
+    fn does_en_passant_reveal_check(&self, position: &Position) -> bool {
+        let player_to_move = position.player_to_move();
+        let opposing_player = player_to_move.other();
+
+        if position.king_square(opposing_player).rank()
+            != Rank::PAWN_DOUBLE_PUSH_TARGET_RANKS[player_to_move as usize]
+        {
+            return false;
+        }
+        false
     }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::{assert_move_list, position::DiagramFormatter, test_position, Move, MoveBuilder};
-    use chessfriend_core::{piece, Color, Piece, Square};
+    use crate::{
+        assert_move_list, formatted_move_list, position::DiagramFormatter, test_position,
+        testing::*,
+    };
+    use chessfriend_core::{piece, Color, Square};
+    use chessfriend_moves::{Builder as MoveBuilder, Move};
     use std::collections::HashSet;
 
     #[test]
-    fn one_2square_push() {
+    fn one_double_push() -> TestResult {
         let pos = test_position![White Pawn on E2];
 
         let generator = PawnMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
+        let pawn = piece!(White Pawn on E2);
         let expected_moves = HashSet::from_iter([
-            MoveBuilder::new(piece!(White Pawn), Square::E2, Square::E3).build(),
-            MoveBuilder::new(piece!(White Pawn), Square::E2, Square::E4).build(),
+            MoveBuilder::push(&pawn).to(Square::E3).build()?,
+            MoveBuilder::double_push(pawn.square().file(), pawn.color()).build()?,
         ]);
 
-        let generated_moves: HashSet<Move> = generator.iter().collect();
+        let generated_moves: HashSet<_> = generator.iter().collect();
 
-        assert_eq!(generated_moves, expected_moves);
+        assert_move_list!(generated_moves, expected_moves, pos);
+
+        Ok(())
     }
 
     #[test]
-    fn one_1square_push() {
+    fn one_single_push() -> TestResult {
         let pos = test_position![White Pawn on E3];
 
         let generator = PawnMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
+        let generated_moves: HashSet<_> = generator.iter().collect();
 
-        let expected_moves = HashSet::from_iter([MoveBuilder::new(
-            Piece::pawn(Color::White),
-            Square::E3,
-            Square::E4,
-        )
-        .build()]);
-
-        let generated_moves: HashSet<Move> = generator.iter().collect();
+        let expected_moves = HashSet::from_iter([MoveBuilder::push(&piece!(White Pawn on E3))
+            .to(Square::E4)
+            .build()?]);
 
         assert_move_list!(generated_moves, expected_moves, pos);
+
+        Ok(())
     }
 
     #[test]
-    fn one_obstructed_2square_push() {
+    fn one_obstructed_2square_push() -> TestResult {
         let pos = test_position![
             White Pawn on E2,
             White Knight on E4,
@@ -124,16 +227,15 @@ mod tests {
 
         let generator = PawnMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
-        let expected_moves = HashSet::from_iter([MoveBuilder::new(
-            Piece::pawn(Color::White),
-            Square::E2,
-            Square::E3,
-        )
-        .build()]);
+        let expected_moves = HashSet::from_iter([MoveBuilder::push(&piece!(White Pawn on E2))
+            .to(Square::E3)
+            .build()?]);
 
-        let generated_moves: HashSet<Move> = generator.iter().collect();
+        let generated_moves: HashSet<_> = generator.iter().collect();
 
         assert_move_list!(generated_moves, expected_moves, pos);
+
+        Ok(())
     }
 
     #[test]
@@ -145,14 +247,14 @@ mod tests {
 
         let generator = PawnMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
-        let generated_moves: HashSet<Move> = generator.iter().collect();
-        let expected_moves: HashSet<Move> = HashSet::new();
+        let generated_moves: HashSet<_> = generator.iter().collect();
+        let expected_moves: HashSet<_> = HashSet::new();
 
         assert_move_list!(generated_moves, expected_moves, pos);
     }
 
     #[test]
-    fn one_attack() {
+    fn one_attack() -> TestResult {
         let pos = test_position![
             White Pawn on E4,
             White Bishop on E5,
@@ -161,20 +263,19 @@ mod tests {
 
         let generator = PawnMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
-        let expected_moves =
-            HashSet::from_iter(
-                [MoveBuilder::new(piece!(White Pawn), Square::E4, Square::D5)
-                    .capturing(piece!(Black Knight on D5))
-                    .build()],
-            );
+        let expected_moves = HashSet::from_iter([MoveBuilder::push(&piece!(White Pawn on E4))
+            .capturing_on(Square::D5)
+            .build()?]);
 
-        let generated_moves: HashSet<Move> = generator.iter().collect();
+        let generated_moves: HashSet<_> = generator.iter().collect();
 
-        assert_eq!(generated_moves, expected_moves);
+        assert_move_list!(generated_moves, expected_moves, pos);
+
+        Ok(())
     }
 
     #[test]
-    fn one_double_attack() {
+    fn one_double_attack() -> TestResult {
         let pos = test_position![
             White Pawn on E4,
             White Bishop on E5,
@@ -184,21 +285,68 @@ mod tests {
 
         let generator = PawnMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
+        let builder = MoveBuilder::push(&piece!(White Pawn on E4));
         let expected_moves = HashSet::from_iter([
-            MoveBuilder::new(piece!(White Pawn), Square::E4, Square::D5)
-                .capturing(piece!(Black Knight on D5))
-                .build(),
-            MoveBuilder::new(piece!(White Pawn), Square::E4, Square::F5)
-                .capturing(piece!(Black Queen on F5))
-                .build(),
+            builder.clone().capturing_on(Square::D5).build()?,
+            builder.clone().capturing_on(Square::F5).build()?,
         ]);
 
-        let generated_moves: HashSet<Move> = generator.iter().collect();
+        let generated_moves: HashSet<_> = generator.iter().collect();
 
         assert_eq!(
             generated_moves, expected_moves,
             "generated: {:#?}\nexpected: {:#?}",
             generated_moves, expected_moves
         );
+
+        Ok(())
+    }
+
+    #[test]
+    fn one_en_passant_attack() -> TestResult {
+        let pos = test_position!(Black, [
+            White Pawn on D4,
+            Black Pawn on E4,
+        ], D3);
+
+        let generator = PawnMoveGenerator::new(&pos, Color::Black, BitBoard::FULL, BitBoard::FULL);
+        let generated_moves: HashSet<Move> = generator.iter().collect();
+
+        let builder = MoveBuilder::push(&piece!(Black Pawn on E4));
+        let expected_moves = HashSet::from_iter([
+            builder.capturing_en_passant_on(Square::D3).build()?,
+            builder.clone().to(Square::E3).build()?,
+        ]);
+
+        assert_move_list!(generated_moves, expected_moves, pos);
+
+        Ok(())
+    }
+
+    /// Make sure the player cannot capture en passant if doing so would not resolve the check.
+    #[test]
+    fn cannot_capture_en_passant_while_in_check() -> TestResult {
+        let pos = test_position!(Black, [
+            Black King on B5,
+            Black Pawn on E4,
+            White Pawn on D4,
+            White Rook on B1,
+        ], D3);
+
+        assert!(pos.is_king_in_check());
+
+        let generated_moves: HashSet<_> = pos.moves().iter().collect();
+
+        assert!(
+            !generated_moves.contains(
+                &MoveBuilder::push(&piece!(Black Pawn on E4))
+                    .capturing_en_passant_on(Square::D3)
+                    .build()?
+            ),
+            "Valid moves: {:?}",
+            formatted_move_list!(generated_moves, pos)
+        );
+
+        Ok(())
     }
 }
diff --git a/position/src/move_generator/queen.rs b/position/src/move_generator/queen.rs
index 0b8a571..e0817cb 100644
--- a/position/src/move_generator/queen.rs
+++ b/position/src/move_generator/queen.rs
@@ -75,7 +75,7 @@ mod tests {
 
         let generator =
             ClassicalMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
-        let bitboard = generator.bitboard();
+        let bitboard = generator._test_bitboard();
         let expected = bitboard![
             A2, C2, D2, E2, F2, G2, H2, // Rank
             B1, B3, B4, B5, B6, B7, B8, // File
@@ -102,7 +102,7 @@ mod tests {
 
         let generator =
             ClassicalMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
-        let bitboard = generator.bitboard();
+        let bitboard = generator._test_bitboard();
         let expected = BitBoard::new(
             0b10000001_01000001_00100001_00010001_00001001_00000101_00000011_00001110,
         );
@@ -127,7 +127,7 @@ mod tests {
             ClassicalMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
         assert_eq!(
-            generator.bitboard(),
+            generator._test_bitboard(),
             bitboard![
                 A2, C2, D2, E2, F2, G2, H2, // Rank
                 B1, B3, B4, B5, B6, B7, B8, // File
@@ -146,7 +146,7 @@ mod tests {
             ClassicalMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
         assert_eq!(
-            generator.bitboard(),
+            generator._test_bitboard(),
             bitboard![
                 A3, B3, C3, E3, F3, G3, H3, // Rank
                 D1, D2, D4, D5, D6, D7, D8, // File
diff --git a/position/src/move_generator/rook.rs b/position/src/move_generator/rook.rs
index 8e9037a..f692da5 100644
--- a/position/src/move_generator/rook.rs
+++ b/position/src/move_generator/rook.rs
@@ -73,7 +73,7 @@ mod tests {
             ClassicalMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
         assert_eq!(
-            generator.bitboard(),
+            generator._test_bitboard(),
             bitboard![A1, A3, A4, A5, A6, A7, A8, B2, C2, D2, E2, F2, G2, H2]
         );
     }
@@ -92,7 +92,7 @@ mod tests {
             ClassicalMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
         assert_eq!(
-            generator.bitboard(),
+            generator._test_bitboard(),
             BitBoard::new(
                 0b00000001_00000001_00000001_00000001_00000001_00000001_00000001_00001110
             )
@@ -111,7 +111,7 @@ mod tests {
             ClassicalMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
         assert_eq!(
-            generator.bitboard(),
+            generator._test_bitboard(),
             bitboard![A2, A3, A4, A5, A6, A7, A8, B1, C1, D1, E1]
         );
     }
@@ -124,7 +124,7 @@ mod tests {
             ClassicalMoveGenerator::new(&pos, Color::White, BitBoard::FULL, BitBoard::FULL);
 
         assert_eq!(
-            generator.bitboard(),
+            generator._test_bitboard(),
             bitboard![A4, B4, C4, E4, F4, G4, H4, D1, D2, D3, D5, D6, D7, D8]
         );
     }
diff --git a/position/src/move_generator/tests/peterellisjones.rs b/position/src/move_generator/tests/peterellisjones.rs
index 3828970..4a12b92 100644
--- a/position/src/move_generator/tests/peterellisjones.rs
+++ b/position/src/move_generator/tests/peterellisjones.rs
@@ -6,15 +6,13 @@
 //! [1]: https://peterellisjones.com
 //! [2]: https://peterellisjones.com/posts/generating-legal-chess-moves-efficiently/
 
-use crate::{
-    assert_move_list, formatted_move_list, move_generator::Moves, r#move::AlgebraicMoveFormatter,
-    test_position, Move, MoveBuilder,
-};
+use crate::{assert_move_list, formatted_move_list, test_position, testing::*};
 use chessfriend_core::{piece, Square};
+use chessfriend_moves::Builder as MoveBuilder;
 use std::collections::HashSet;
 
 #[test]
-fn pseudo_legal_move_generation() -> Result<(), String> {
+fn pseudo_legal_move_generation() -> TestResult {
     let pos = test_position!(Black, [
         Black King on E8,
         White King on E1,
@@ -24,7 +22,7 @@ fn pseudo_legal_move_generation() -> Result<(), String> {
     let generated_moves = pos.moves();
     let king_moves = generated_moves
         .moves_for_piece(&piece!(Black King on E8))
-        .ok_or("No valid king moves")?;
+        .ok_or(TestError::NoLegalMoves)?;
 
     assert!(!king_moves.can_move_to_square(Square::F8));
     assert!(!king_moves.can_move_to_square(Square::F7));
@@ -33,7 +31,7 @@ fn pseudo_legal_move_generation() -> Result<(), String> {
 }
 
 #[test]
-fn gotcha_king_moves_away_from_a_checking_slider() -> Result<(), String> {
+fn gotcha_king_moves_away_from_a_checking_slider() -> TestResult {
     let pos = test_position!(Black, [
         Black King on E7,
         White King on E1,
@@ -43,7 +41,7 @@ fn gotcha_king_moves_away_from_a_checking_slider() -> Result<(), String> {
     let generated_moves = pos.moves();
     let king_moves = generated_moves
         .moves_for_piece(&piece!(Black King on E7))
-        .ok_or("No valid king moves")?;
+        .ok_or(TestError::NoLegalMoves)?;
 
     assert!(!king_moves.can_move_to_square(Square::E8));
 
@@ -51,7 +49,7 @@ fn gotcha_king_moves_away_from_a_checking_slider() -> Result<(), String> {
 }
 
 #[test]
-fn check_evasions_1() {
+fn check_evasions_1() -> TestResult {
     let pos = test_position!(Black, [
         Black King on E8,
         White King on E1,
@@ -60,11 +58,12 @@ fn check_evasions_1() {
 
     let generated_moves = pos.moves();
 
+    let builder = MoveBuilder::push(&piece!(Black King on E8));
     let expected_moves = HashSet::from_iter([
-        MoveBuilder::new(piece!(Black King), Square::E8, Square::D8).build(),
-        MoveBuilder::new(piece!(Black King), Square::E8, Square::E7).build(),
-        MoveBuilder::new(piece!(Black King), Square::E8, Square::F7).build(),
-        MoveBuilder::new(piece!(Black King), Square::E8, Square::F8).build(),
+        builder.clone().to(Square::D8).build()?,
+        builder.clone().to(Square::E7).build()?,
+        builder.clone().to(Square::F7).build()?,
+        builder.clone().to(Square::F8).build()?,
     ]);
 
     assert_move_list!(
@@ -72,10 +71,12 @@ fn check_evasions_1() {
         expected_moves,
         pos
     );
+
+    Ok(())
 }
 
 #[test]
-fn check_evasions_double_check() {
+fn check_evasions_double_check() -> TestResult {
     let pos = test_position!(Black, [
         Black King on E8,
         Black Bishop on F6,
@@ -86,11 +87,12 @@ fn check_evasions_double_check() {
 
     let generated_moves = pos.moves();
 
+    let builder = MoveBuilder::push(&piece!(Black King on E8));
     let expected_moves = HashSet::from_iter([
-        MoveBuilder::new(piece!(Black King), Square::E8, Square::D8).build(),
-        MoveBuilder::new(piece!(Black King), Square::E8, Square::D7).build(),
-        MoveBuilder::new(piece!(Black King), Square::E8, Square::F7).build(),
-        MoveBuilder::new(piece!(Black King), Square::E8, Square::F8).build(),
+        builder.clone().to(Square::D8).build()?,
+        builder.clone().to(Square::D7).build()?,
+        builder.clone().to(Square::F7).build()?,
+        builder.clone().to(Square::F8).build()?,
     ]);
 
     assert_move_list!(
@@ -98,10 +100,12 @@ fn check_evasions_double_check() {
         expected_moves,
         pos
     );
+
+    Ok(())
 }
 
 #[test]
-fn single_check_with_blocker() {
+fn single_check_with_blocker() -> TestResult {
     let pos = test_position!(Black, [
         Black King on E8,
         Black Knight on G6,
@@ -111,15 +115,15 @@ fn single_check_with_blocker() {
 
     let generated_moves = pos.moves();
 
+    let king_builder = MoveBuilder::push(&piece!(Black King on E8));
+    let knight_builder = MoveBuilder::push(&piece!(Black Knight on G6));
     let expected_moves = HashSet::from_iter([
-        MoveBuilder::new(piece!(Black King), Square::E8, Square::D8).build(),
-        MoveBuilder::new(piece!(Black King), Square::E8, Square::D7).build(),
-        MoveBuilder::new(piece!(Black King), Square::E8, Square::F7).build(),
-        MoveBuilder::new(piece!(Black King), Square::E8, Square::F8).build(),
-        MoveBuilder::new(piece!(Black Knight), Square::G6, Square::E7).build(),
-        MoveBuilder::new(piece!(Black Knight), Square::G6, Square::E5)
-            .capturing(piece!(White Rook on E5))
-            .build(),
+        king_builder.clone().to(Square::D8).build()?,
+        king_builder.clone().to(Square::D7).build()?,
+        king_builder.clone().to(Square::F7).build()?,
+        king_builder.clone().to(Square::F8).build()?,
+        knight_builder.clone().to(Square::E7).build()?,
+        knight_builder.clone().capturing_on(Square::E5).build()?,
     ]);
 
     assert_move_list!(
@@ -127,10 +131,12 @@ fn single_check_with_blocker() {
         expected_moves,
         pos
     );
+
+    Ok(())
 }
 
 #[test]
-fn en_passant_check_capture() {
+fn en_passant_check_capture() -> TestResult {
     let pos = test_position!(Black, [
         Black King on C5,
         Black Pawn on E4,
@@ -139,21 +145,23 @@ fn en_passant_check_capture() {
 
     assert!(pos.is_king_in_check());
 
-    let generated_moves = pos.moves().iter().collect::<HashSet<_>>();
+    let generated_moves: HashSet<_> = pos.moves().iter().collect();
 
     assert!(
         generated_moves.contains(
-            &MoveBuilder::new(piece!(Black Pawn), Square::E4, Square::D3)
-                .capturing_en_passant(piece!(White Pawn on D4))
-                .build()
+            &MoveBuilder::push(&piece!(Black Pawn on E4))
+                .capturing_en_passant_on(Square::D3)
+                .build()?
         ),
         "Valid moves: {:?}",
         formatted_move_list!(generated_moves, pos)
     );
+
+    Ok(())
 }
 
 #[test]
-fn en_passant_check_block() {
+fn en_passant_check_block() -> TestResult {
     let pos = test_position!(Black, [
         Black King on B5,
         Black Pawn on E4,
@@ -163,21 +171,23 @@ fn en_passant_check_block() {
 
     assert!(pos.is_king_in_check());
 
-    let generated_moves = pos.moves().iter().collect::<HashSet<_>>();
+    let generated_moves: HashSet<_> = pos.moves().iter().collect();
 
     assert!(
         generated_moves.contains(
-            &MoveBuilder::new(piece!(Black Pawn), Square::E4, Square::D3)
-                .capturing_en_passant(piece!(White Pawn on D4))
-                .build()
+            &MoveBuilder::push(&piece!(Black Pawn on E4))
+                .capturing_en_passant_on(Square::D3)
+                .build()?
         ),
         "Valid moves: {:?}",
         formatted_move_list!(generated_moves, pos)
     );
+
+    Ok(())
 }
 
 #[test]
-fn pinned_pieces_rook_cannot_move_out_of_pin() -> Result<(), String> {
+fn pinned_pieces_rook_cannot_move_out_of_pin() -> TestResult {
     let pos = test_position!(Black, [
         Black King on E8,
         Black Rook on E6,
@@ -190,21 +200,21 @@ fn pinned_pieces_rook_cannot_move_out_of_pin() -> Result<(), String> {
     let generated_moves = pos.moves();
     let rook_moves = generated_moves
         .moves_for_piece(&piece!(Black Rook on E6))
-        .ok_or("No valid rook moves")?;
+        .ok_or(TestError::NoLegalMoves)?;
 
     assert!(!rook_moves.can_move_to_square(Square::D6));
     assert!(!rook_moves.can_move_to_square(Square::F6));
 
-    assert!(rook_moves.can_move_to_square(Square::E7));
-    assert!(rook_moves.can_move_to_square(Square::E5));
-    assert!(rook_moves.can_move_to_square(Square::E4));
     assert!(rook_moves.can_move_to_square(Square::E3));
+    assert!(rook_moves.can_move_to_square(Square::E4));
+    assert!(rook_moves.can_move_to_square(Square::E5));
+    assert!(rook_moves.can_move_to_square(Square::E7));
 
     Ok(())
 }
 
 #[test]
-fn en_passant_discovered_check() {
+fn en_passant_discovered_check() -> TestResult {
     let pos = test_position!(Black, [
         Black King on A4,
         Black Pawn on E4,
@@ -212,15 +222,17 @@ fn en_passant_discovered_check() {
         White Queen on H4,
     ], D3);
 
-    let generated_moves = pos.moves().iter().collect::<HashSet<_>>();
+    let generated_moves: HashSet<_> = pos.moves().iter().collect();
 
-    let unexpected_move = MoveBuilder::new(piece!(Black Pawn), Square::E4, Square::D3)
-        .capturing_en_passant(piece!(White Pawn on D4))
-        .build();
+    let unexpected_move = MoveBuilder::push(&piece!(Black Pawn on E4))
+        .capturing_en_passant_on(Square::D3)
+        .build()?;
 
     assert!(
         !generated_moves.contains(&unexpected_move),
         "Valid moves: {:?}",
         formatted_move_list!(generated_moves, pos)
     );
+
+    Ok(())
 }
diff --git a/position/src/move_generator/tests/single_pieces.rs b/position/src/move_generator/tests/single_pieces.rs
index 01a3e34..f8d06fb 100644
--- a/position/src/move_generator/tests/single_pieces.rs
+++ b/position/src/move_generator/tests/single_pieces.rs
@@ -1,36 +1,32 @@
 // Eryn Wells <eryn@erynwells.me>
 
-use crate::{position, r#move::AlgebraicMoveFormatter, Move, MoveBuilder};
+use crate::{assert_move_list, test_position, testing::*};
 use chessfriend_core::{piece, Square};
+use chessfriend_moves::Builder as MoveBuilder;
 use std::collections::HashSet;
 
 #[test]
-fn one_king() {
-    let pos = position![
+fn one_king() -> TestResult {
+    let pos = test_position![
         White King on D3,
         Black King on H6,
     ];
 
+    let builder = MoveBuilder::push(&piece!(White King on D3));
     let expected_moves = HashSet::from_iter([
-        MoveBuilder::new(piece!(White King), Square::D3, Square::D4).build(),
-        MoveBuilder::new(piece!(White King), Square::D3, Square::E4).build(),
-        MoveBuilder::new(piece!(White King), Square::D3, Square::E3).build(),
-        MoveBuilder::new(piece!(White King), Square::D3, Square::E2).build(),
-        MoveBuilder::new(piece!(White King), Square::D3, Square::D2).build(),
-        MoveBuilder::new(piece!(White King), Square::D3, Square::C2).build(),
-        MoveBuilder::new(piece!(White King), Square::D3, Square::C3).build(),
-        MoveBuilder::new(piece!(White King), Square::D3, Square::C4).build(),
+        builder.clone().to(Square::D4).build()?,
+        builder.clone().to(Square::E4).build()?,
+        builder.clone().to(Square::E3).build()?,
+        builder.clone().to(Square::E2).build()?,
+        builder.clone().to(Square::D2).build()?,
+        builder.clone().to(Square::C2).build()?,
+        builder.clone().to(Square::C3).build()?,
+        builder.clone().to(Square::C4).build()?,
     ]);
 
-    let generated_moves: HashSet<Move> = pos.moves().iter().collect();
+    let generated_moves: HashSet<_> = pos.moves().iter().collect();
 
-    assert_eq!(
-        generated_moves,
-        expected_moves,
-        "{:?}",
-        generated_moves
-            .symmetric_difference(&expected_moves)
-            .map(|m| format!("{}", AlgebraicMoveFormatter::new(&m, &pos)))
-            .collect::<Vec<String>>()
-    );
+    assert_move_list!(generated_moves, expected_moves, pos);
+
+    Ok(())
 }
diff --git a/position/src/position/builders/mod.rs b/position/src/position/builders/mod.rs
index 9324249..ea1f60d 100644
--- a/position/src/position/builders/mod.rs
+++ b/position/src/position/builders/mod.rs
@@ -3,5 +3,5 @@
 mod move_builder;
 mod position_builder;
 
-pub use move_builder::Builder as MoveBuilder;
+pub use move_builder::{Builder as MoveBuilder, MakeMoveError};
 pub use position_builder::Builder as PositionBuilder;
diff --git a/position/src/position/builders/move_builder.rs b/position/src/position/builders/move_builder.rs
index c926c08..307bae6 100644
--- a/position/src/position/builders/move_builder.rs
+++ b/position/src/position/builders/move_builder.rs
@@ -1,12 +1,19 @@
 // Eryn Wells <eryn@erynwells.me>
 
-use crate::{
-    position::flags::Flags,
-    r#move::{AlgebraicMoveFormatter, Castle},
-    MakeMoveError, Move, Position,
-};
+use crate::{position::flags::Flags, Position};
 use chessfriend_bitboard::BitBoard;
 use chessfriend_core::{Color, Direction, Piece, PlacedPiece, Shape, Square};
+use chessfriend_moves::{Castle, EnPassant, Move};
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum MakeMoveError {
+    PlayerOutOfTurn,
+    NoPiece,
+    NoCapturedPiece,
+    NoLegalMoves,
+    IllegalCastle,
+    IllegalSquare(Square),
+}
 
 /// A position builder that builds a new position by making a move.
 #[derive(Clone)]
@@ -27,7 +34,7 @@ pub enum ValidatedMove {
         captured_piece: Option<PlacedPiece>,
         promotion: Option<Shape>,
         flags: Flags,
-        en_passant_square: Option<Square>,
+        en_passant: Option<EnPassant>,
         increment_ply: bool,
     },
     Castle {
@@ -55,14 +62,14 @@ where
     M: MoveToMake,
 {
     pub fn make(self, mv: &Move) -> Result<Builder<'p, ValidatedMove>, MakeMoveError> {
-        let from_square = mv.from_square();
+        let origin_square = mv.origin_square();
 
         let piece = self
             .position
-            .piece_on_square(from_square)
+            .piece_on_square(origin_square)
             .ok_or(MakeMoveError::NoPiece)?;
 
-        let to_square = mv.to_square();
+        let target_square = mv.target_square();
 
         let moves = self
             .position
@@ -76,8 +83,8 @@ where
                 }
             }
             None => {
-                if !moves.can_move_to_square(to_square) {
-                    return Err(MakeMoveError::IllegalSquare(to_square));
+                if !moves.can_move_to_square(target_square) {
+                    return Err(MakeMoveError::IllegalSquare(target_square));
                 }
             }
         }
@@ -87,8 +94,8 @@ where
         let captured_piece = if mv.is_en_passant() {
             // En passant captures the pawn directly ahead (in the player's direction) of the en passant square.
             let capture_square = match player {
-                Color::White => to_square.neighbor(Direction::South),
-                Color::Black => to_square.neighbor(Direction::North),
+                Color::White => target_square.neighbor(Direction::South),
+                Color::Black => target_square.neighbor(Direction::North),
             }
             .ok_or(MakeMoveError::NoCapturedPiece)?;
 
@@ -100,7 +107,7 @@ where
         } else if mv.is_capture() {
             Some(
                 self.position
-                    .piece_on_square(to_square)
+                    .piece_on_square(target_square)
                     .ok_or(MakeMoveError::NoCapturedPiece)?,
             )
         } else {
@@ -142,11 +149,12 @@ where
                 },
             })
         } else {
-            let en_passant_square: Option<Square> = if mv.is_double_push() {
+            let en_passant = if mv.is_double_push() {
                 match piece.color() {
-                    Color::White => to_square.neighbor(Direction::South),
-                    Color::Black => to_square.neighbor(Direction::North),
+                    Color::White => target_square.neighbor(Direction::South),
+                    Color::Black => target_square.neighbor(Direction::North),
                 }
+                .and_then(EnPassant::from_target_square)
             } else {
                 None
             };
@@ -154,13 +162,13 @@ where
             Ok(Builder {
                 position: self.position,
                 move_to_make: ValidatedMove::RegularMove {
-                    from_square,
-                    to_square,
+                    from_square: origin_square,
+                    to_square: target_square,
                     moving_piece: piece,
                     captured_piece,
                     promotion: mv.promotion(),
                     flags,
-                    en_passant_square,
+                    en_passant,
                     increment_ply: !(mv.is_capture() || piece.is_pawn()),
                 },
             })
@@ -183,7 +191,7 @@ impl<'p> Builder<'p, ValidatedMove> {
                 captured_piece,
                 promotion,
                 flags,
-                en_passant_square,
+                en_passant,
                 increment_ply,
             } => {
                 let mut pieces = self.position.piece_bitboards().clone();
@@ -210,7 +218,7 @@ impl<'p> Builder<'p, ValidatedMove> {
                     self.position.player_to_move().other(),
                     flags,
                     pieces,
-                    en_passant_square,
+                    en_passant,
                     ply,
                     updated_move_number,
                 )
@@ -223,18 +231,19 @@ impl<'p> Builder<'p, ValidatedMove> {
             } => {
                 let mut pieces = self.position.piece_bitboards().clone();
 
-                let target_squares = castle.target_squares(player);
+                let parameters = castle.parameters(player);
 
-                let king_from: BitBoard = king.square().into();
-                let king_to: BitBoard = target_squares.king.into();
-                *pieces.bitboard_for_piece_mut(king.piece()) ^= king_from | king_to;
+                let king_origin_square: BitBoard = king.square().into();
+                let king_target_square: BitBoard = parameters.king_target_square().into();
+                *pieces.bitboard_for_piece_mut(king.piece()) ^=
+                    king_origin_square | king_target_square;
 
                 let rook_from: BitBoard = rook.square().into();
-                let rook_to: BitBoard = target_squares.rook.into();
+                let rook_to: BitBoard = parameters.rook_target_square().into();
                 *pieces.bitboard_for_piece_mut(rook.piece()) ^= rook_from | rook_to;
 
                 *pieces.bitboard_for_color_mut(player) &=
-                    !(king_from | rook_from) | (king_to | rook_to);
+                    !(king_origin_square | rook_from) | (king_target_square | rook_to);
 
                 Position::new(
                     player.other(),
@@ -261,15 +270,24 @@ impl<'p> From<&'p Position> for Builder<'p, NoMove> {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::{position, r#move::Castle, MoveBuilder, PositionBuilder};
-    use chessfriend_core::piece;
+    use crate::testing::*;
+    use crate::{position, test_position};
+    use chessfriend_core::{piece, File};
+    use chessfriend_moves::Builder as MoveBuilder;
 
     #[test]
-    fn move_white_pawn_one_square() -> Result<(), MakeMoveError> {
+    fn move_white_pawn_one_square() -> TestResult {
         let pos = position![White Pawn on E2];
-        let mv = MoveBuilder::new(piece!(White Pawn), Square::E2, Square::E3).build();
+        let mv = MoveBuilder::new()
+            .from(Square::E2)
+            .to(Square::E3)
+            .build()
+            .map_err(TestError::BuildMove)?;
 
-        let new_position = Builder::<NoMove>::new(&pos).make(&mv)?.build();
+        let new_position = Builder::<NoMove>::new(&pos)
+            .make(&mv)
+            .map_err(|err| TestError::MakeMove(err))?
+            .build();
         println!("{}", &new_position);
 
         assert_eq!(
@@ -281,25 +299,32 @@ mod tests {
     }
 
     #[test]
-    fn move_white_pawn_two_squares() -> Result<(), MakeMoveError> {
-        let pos = position![White Pawn on E2];
-        let mv = MoveBuilder::new(piece!(White Pawn), Square::E2, Square::E4).build();
+    fn move_white_pawn_two_squares() -> TestResult {
+        let pos = test_position![White Pawn on E2];
 
-        let new_position = Builder::<NoMove>::new(&pos).make(&mv)?.build();
+        let mv = MoveBuilder::double_push(File::E, Color::White).build()?;
+
+        let new_position = Builder::new(&pos).make(&mv)?.build();
         println!("{}", &new_position);
 
         assert_eq!(
             new_position.piece_on_square(Square::E4),
             Some(piece!(White Pawn on E4))
         );
-        assert_eq!(new_position.en_passant_square(), Some(Square::E3));
+
+        let en_passant = new_position.en_passant();
+        assert!(en_passant.is_some());
+        assert_eq!(
+            en_passant.as_ref().map(EnPassant::target_square),
+            Some(Square::E3)
+        );
 
         Ok(())
     }
 
     #[test]
-    fn white_kingside_castle() -> Result<(), MakeMoveError> {
-        let pos = position![
+    fn white_kingside_castle() -> TestResult {
+        let pos = test_position![
             White King on E1,
             White Rook on H1,
             White Pawn on E2,
@@ -307,13 +332,10 @@ mod tests {
             White Pawn on G2,
             White Pawn on H2
         ];
-        println!("{}", &pos);
 
-        let mv = MoveBuilder::new(piece!(White King), Square::E1, Square::G1)
-            .castle(Castle::KingSide)
-            .build();
+        let mv = MoveBuilder::castling(Color::White, Castle::KingSide).build()?;
 
-        let new_position = Builder::<NoMove>::new(&pos).make(&mv)?.build();
+        let new_position = Builder::new(&pos).make(&mv)?.build();
         println!("{}", &new_position);
 
         assert_eq!(
@@ -329,15 +351,14 @@ mod tests {
     }
 
     #[test]
-    fn en_passant_capture() -> Result<(), MakeMoveError> {
-        let pos = PositionBuilder::new()
-            .place_piece(piece!(White Pawn on B5))
-            .place_piece(piece!(Black Pawn on A7))
-            .to_move(Color::Black)
-            .build();
-        println!("{pos}");
+    fn en_passant_capture() -> TestResult {
+        let pos = test_position!(Black, [
+            White Pawn on B5,
+            Black Pawn on A7,
+        ]);
+
+        let black_pawn_move = MoveBuilder::double_push(File::A, Color::Black).build()?;
 
-        let black_pawn_move = MoveBuilder::new(piece!(Black Pawn), Square::A7, Square::A5).build();
         assert!(black_pawn_move.is_double_push());
         assert!(!black_pawn_move.is_en_passant());
 
@@ -353,10 +374,10 @@ mod tests {
             Some(piece!(White Pawn on B5))
         );
 
-        let white_pawn_capture = MoveBuilder::new(piece!(White Pawn), Square::B5, Square::A6)
-            .capturing_en_passant(piece!(Black Pawn on A5))
-            .build();
-        let en_passant_capture = Builder::<NoMove>::new(&en_passant_position)
+        let white_pawn_capture = MoveBuilder::push(&piece!(White Pawn on B5))
+            .capturing_en_passant_on(Square::A6)
+            .build()?;
+        let en_passant_capture = Builder::new(&en_passant_position)
             .make(&white_pawn_capture)?
             .build();
         println!("{en_passant_capture}");
diff --git a/position/src/position/builders/position_builder.rs b/position/src/position/builders/position_builder.rs
index 5011f21..08fc193 100644
--- a/position/src/position/builders/position_builder.rs
+++ b/position/src/position/builders/position_builder.rs
@@ -2,10 +2,10 @@
 
 use crate::{
     position::{flags::Flags, piece_sets::PieceBitBoards},
-    r#move::Castle,
     Position,
 };
 use chessfriend_core::{piece, Color, Piece, PlacedPiece, Rank, Shape, Square};
+use chessfriend_moves::{Castle, EnPassant};
 use std::collections::BTreeMap;
 
 #[derive(Clone)]
@@ -14,7 +14,7 @@ pub struct Builder {
     flags: Flags,
     pieces: BTreeMap<Square, Piece>,
     kings: [Option<Square>; 2],
-    en_passant_square: Option<Square>,
+    en_passant: Option<EnPassant>,
     ply_counter: u16,
     move_number: u16,
 }
@@ -30,7 +30,7 @@ impl Builder {
             flags: Flags::default(),
             pieces: BTreeMap::default(),
             kings: [None, None],
-            en_passant_square: None,
+            en_passant: None,
             ply_counter: 0,
             move_number: 1,
         }
@@ -52,7 +52,7 @@ impl Builder {
             flags: position.flags(),
             pieces,
             kings: [Some(white_king), Some(black_king)],
-            en_passant_square: position.en_passant_square(),
+            en_passant: position.en_passant(),
             ply_counter: position.ply_counter(),
             move_number: position.move_number(),
         }
@@ -73,8 +73,8 @@ impl Builder {
         self
     }
 
-    pub fn en_passant_square(&mut self, square: Option<Square>) -> &mut Self {
-        self.en_passant_square = square;
+    pub fn en_passant(&mut self, en_passant: Option<EnPassant>) -> &mut Self {
+        self.en_passant = en_passant;
         self
     }
 
@@ -120,13 +120,13 @@ impl Builder {
 
         for color in Color::ALL {
             for castle in Castle::ALL {
-                let starting_squares = castle.starting_squares(color);
+                let parameters = castle.parameters(color);
                 let has_rook_on_starting_square = self
                     .pieces
-                    .get(&starting_squares.rook)
+                    .get(&parameters.rook_origin_square())
                     .is_some_and(|piece| piece.shape() == Shape::Rook);
                 let king_is_on_starting_square =
-                    self.kings[color as usize] == Some(starting_squares.king);
+                    self.kings[color as usize] == Some(parameters.king_origin_square());
 
                 if !king_is_on_starting_square || !has_rook_on_starting_square {
                     flags.clear_player_has_right_to_castle_flag(color, castle);
@@ -138,7 +138,7 @@ impl Builder {
             self.player_to_move,
             flags,
             pieces,
-            self.en_passant_square,
+            self.en_passant,
             self.ply_counter,
             self.move_number,
         )
@@ -173,7 +173,7 @@ impl Default for Builder {
             flags: Flags::default(),
             pieces: pieces,
             kings: [Some(white_king_square), Some(black_king_square)],
-            en_passant_square: None,
+            en_passant: None,
             ply_counter: 0,
             move_number: 1,
         }
diff --git a/position/src/position/flags.rs b/position/src/position/flags.rs
index 47e49bf..19d3165 100644
--- a/position/src/position/flags.rs
+++ b/position/src/position/flags.rs
@@ -1,7 +1,7 @@
 // Eryn Wells <eryn@erynwells.me>
 
-use crate::r#move::Castle;
 use chessfriend_core::Color;
+use chessfriend_moves::Castle;
 use std::fmt;
 
 #[derive(Clone, Copy, Eq, Hash, PartialEq)]
@@ -10,7 +10,7 @@ pub struct Flags(u8);
 impl Flags {
     #[inline]
     pub(super) fn player_has_right_to_castle_flag_offset(color: Color, castle: Castle) -> usize {
-        ((color as usize) << 1) + castle.into_index()
+        ((color as usize) << 1) + castle as usize
     }
 
     pub(super) fn player_has_right_to_castle(&self, color: Color, castle: Castle) -> bool {
@@ -45,8 +45,6 @@ impl Default for Flags {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::r#move::Castle;
-    use chessfriend_core::Color;
 
     #[test]
     fn castle_flags() {
diff --git a/position/src/position/mod.rs b/position/src/position/mod.rs
index 8ece091..644ccc1 100644
--- a/position/src/position/mod.rs
+++ b/position/src/position/mod.rs
@@ -9,7 +9,7 @@ mod pieces;
 mod position;
 
 pub use {
-    builders::{MoveBuilder, PositionBuilder},
+    builders::{MakeMoveError, MoveBuilder, PositionBuilder},
     diagram_formatter::DiagramFormatter,
     pieces::Pieces,
     position::Position,
diff --git a/position/src/position/position.rs b/position/src/position/position.rs
index 01de793..a6fc369 100644
--- a/position/src/position/position.rs
+++ b/position/src/position/position.rs
@@ -5,11 +5,11 @@ use crate::{
     check::CheckingPieces,
     move_generator::{MoveSet, Moves},
     position::DiagramFormatter,
-    r#move::Castle,
     sight::SightExt,
 };
 use chessfriend_bitboard::BitBoard;
 use chessfriend_core::{Color, Piece, PlacedPiece, Shape, Square};
+use chessfriend_moves::{Castle, EnPassant};
 use std::{cell::OnceCell, fmt};
 
 #[derive(Clone, Debug, Eq)]
@@ -17,7 +17,7 @@ pub struct Position {
     color_to_move: Color,
     flags: Flags,
     pieces: PieceBitBoards,
-    en_passant_square: Option<Square>,
+    en_passant: Option<EnPassant>,
     moves: OnceCell<Moves>,
     half_move_counter: u16,
     full_move_number: u16,
@@ -92,7 +92,7 @@ impl Position {
             return false;
         }
 
-        let castling_parameters = castle.parameters();
+        let castling_parameters = castle.parameters(player);
 
         let all_pieces = self.occupied_squares();
         if !(all_pieces & castling_parameters.clear_squares()).is_empty() {
@@ -182,12 +182,16 @@ impl Position {
         Pieces::new(&self, color)
     }
 
-    pub fn en_passant_square(&self) -> Option<Square> {
-        self.en_passant_square
+    pub fn has_en_passant_square(&self) -> bool {
+        self.en_passant.is_some()
+    }
+
+    pub fn en_passant(&self) -> Option<EnPassant> {
+        self.en_passant
     }
 
     fn _sight_of_player(&self, player: Color, pieces: &PieceBitBoards) -> BitBoard {
-        let en_passant_square = self.en_passant_square;
+        let en_passant_target_square = self.en_passant.map(|ep| ep.target_square());
 
         Shape::ALL
             .iter()
@@ -202,7 +206,7 @@ impl Position {
             })
             .flat_map(|(piece, &bitboard)| {
                 bitboard.occupied_squares().map(move |square| {
-                    PlacedPiece::new(piece, square).sight(pieces, en_passant_square)
+                    PlacedPiece::new(piece, square).sight(pieces, en_passant_target_square)
                 })
             })
             .fold(BitBoard::empty(), |acc, sight| acc | sight)
@@ -214,7 +218,7 @@ impl Position {
 
     #[cfg(test)]
     pub(crate) fn sight_of_piece(&self, piece: &PlacedPiece) -> BitBoard {
-        piece.sight(&self.pieces, self.en_passant_square)
+        piece.sight(&self.pieces, self.en_passant.map(|ep| ep.target_square()))
     }
 
     /// A bitboard representing the squares where a king of the given color will
@@ -295,14 +299,14 @@ impl Position {
         player_to_move: Color,
         flags: Flags,
         pieces: PieceBitBoards,
-        en_passant_square: Option<Square>,
+        en_passant: Option<EnPassant>,
         half_move_counter: u16,
         full_move_number: u16,
     ) -> Self {
         Self {
             color_to_move: player_to_move,
             flags,
-            en_passant_square,
+            en_passant,
             pieces,
             half_move_counter,
             full_move_number,
@@ -332,8 +336,8 @@ impl Position {
 
 #[cfg(test)]
 impl Position {
-    pub(crate) fn test_set_en_passant_square(&mut self, square: Square) {
-        self.en_passant_square = Some(square);
+    pub(crate) fn test_set_en_passant(&mut self, en_passant: EnPassant) {
+        self.en_passant = Some(en_passant);
     }
 }
 
@@ -343,7 +347,7 @@ impl Default for Position {
             color_to_move: Color::White,
             flags: Flags::default(),
             pieces: PieceBitBoards::default(),
-            en_passant_square: None,
+            en_passant: None,
             moves: OnceCell::new(),
             half_move_counter: 0,
             full_move_number: 1,
@@ -356,7 +360,7 @@ impl PartialEq for Position {
         self.pieces == other.pieces
             && self.color_to_move == other.color_to_move
             && self.flags == other.flags
-            && self.en_passant_square == other.en_passant_square
+            && self.en_passant == other.en_passant
     }
 }
 
@@ -368,9 +372,10 @@ impl fmt::Display for Position {
 
 #[cfg(test)]
 mod tests {
-    use crate::{position, test_position, Castle, Position, PositionBuilder};
+    use super::*;
+    use crate::{position, test_position, Position, PositionBuilder};
     use chessfriend_bitboard::bitboard;
-    use chessfriend_core::{piece, Color, Square};
+    use chessfriend_core::piece;
 
     #[test]
     fn piece_on_square() {
diff --git a/position/src/sight.rs b/position/src/sight.rs
index 056ae45..29cbf91 100644
--- a/position/src/sight.rs
+++ b/position/src/sight.rs
@@ -242,6 +242,7 @@ mod tests {
         use crate::test_position;
         use chessfriend_bitboard::{bitboard, BitBoard};
         use chessfriend_core::{piece, Square};
+        use chessfriend_moves::EnPassant;
 
         sight_test!(e4_pawn, piece!(White Pawn on E4), bitboard!(D5, F5));
 
@@ -289,7 +290,7 @@ mod tests {
                 White Pawn on E5,
                 Black Pawn on D5,
             );
-            pos.test_set_en_passant_square(Square::D6);
+            pos.test_set_en_passant(EnPassant::from_target_square(Square::D6).unwrap());
             let piece = piece!(White Pawn on E5);
             let sight = pos.sight_of_piece(&piece);
 
diff --git a/position/src/testing.rs b/position/src/testing.rs
new file mode 100644
index 0000000..1693110
--- /dev/null
+++ b/position/src/testing.rs
@@ -0,0 +1,58 @@
+// Eryn Wells <eryn@erynwells.me>
+
+use crate::MakeMoveError;
+use chessfriend_moves::BuildMoveError;
+
+#[macro_export]
+macro_rules! assert_move_list {
+    ($generated:expr, $expected:expr, $position:expr) => {
+        assert_eq!(
+            $generated,
+            $expected,
+            "\n\tMatching: {:?}\n\tGenerated, not expected: {:?}\n\tExpected, not generated: {:?}",
+            $generated
+                .intersection(&$expected)
+                .map(|mv| format!("{}", mv))
+                .collect::<Vec<String>>(),
+            $generated
+                .difference(&$expected)
+                .map(|mv| format!("{}", mv))
+                .collect::<Vec<String>>(),
+            $expected
+                .difference(&$generated)
+                .map(|mv| format!("{}", mv))
+                .collect::<Vec<String>>(),
+        )
+    };
+}
+
+#[macro_export]
+macro_rules! formatted_move_list {
+    ($move_list:expr, $position:expr) => {
+        $move_list
+            .iter()
+            .map(|mv| format!("{}", mv))
+            .collect::<Vec<String>>()
+    };
+}
+
+pub type TestResult = Result<(), TestError>;
+
+#[derive(Debug, Eq, PartialEq)]
+pub enum TestError {
+    BuildMove(BuildMoveError),
+    MakeMove(MakeMoveError),
+    NoLegalMoves,
+}
+
+impl From<BuildMoveError> for TestError {
+    fn from(value: BuildMoveError) -> Self {
+        TestError::BuildMove(value)
+    }
+}
+
+impl From<MakeMoveError> for TestError {
+    fn from(value: MakeMoveError) -> Self {
+        TestError::MakeMove(value)
+    }
+}
diff --git a/position/src/tests.rs b/position/src/tests.rs
deleted file mode 100644
index 962b9bc..0000000
--- a/position/src/tests.rs
+++ /dev/null
@@ -1,34 +0,0 @@
-// Eryn Wells <eryn@erynwells.me>
-
-#[macro_export]
-macro_rules! assert_move_list {
-    ($generated:expr, $expected:expr, $position:expr) => {
-        assert_eq!(
-            $generated,
-            $expected,
-            "Difference: {:?}",
-            $generated
-                .symmetric_difference(&$expected)
-                .map(|mv| format!(
-                    "{}",
-                    $crate::r#move::AlgebraicMoveFormatter::new(mv, &$position)
-                ))
-                .collect::<Vec<String>>()
-        )
-    };
-}
-
-#[macro_export]
-macro_rules! formatted_move_list {
-    ($move_list:expr, $position:expr) => {
-        $move_list
-            .iter()
-            .map(|mv| {
-                format!(
-                    "{}",
-                    $crate::r#move::AlgebraicMoveFormatter::new(mv, &$position)
-                )
-            })
-            .collect::<Vec<String>>()
-    };
-}