diff --git a/Notes.md b/Notes.md
index 2a809d3..10728be 100644
--- a/Notes.md
+++ b/Notes.md
@@ -4,6 +4,38 @@ Notes on Building Chess Engines
 BitBoards
 ---------
 
+### Mapping
+
+Little-Endian Rank-File (LERF) Mapping maps squares to bit offsets (or indexes) from a1 to h8.
+
+```
+ +-----------------+
+8| 0 0 0 0 0 0 0 0 |
+7| 0 0 0 0 0 0 0 0 |
+6| 0 0 0 0 0 0 0 0 |
+5| 0 0 0 0 0 0 0 0 |
+4| 0 0 0 0 0 0 0 0 |
+3| 0 0 0 0 0 0 0 0 |
+2| 0 0 0 0 0 0 0 0 |
+1| 0 0 0 0 0 0 0 0 |
+ +-----------------+
+   A B C D E F G H
+```
+
+```
+ +-----------------+
+8| 1 0 0 0 0 0 0 0 |
+7| 1 0 0 0 0 0 0 0 |
+6| 1 0 0 0 0 0 0 0 |
+5| 1 0 0 0 0 0 0 0 |
+4| 1 0 0 0 0 0 0 0 |
+3| 1 0 0 0 0 0 0 0 |
+2| 1 0 0 0 0 0 0 0 |
+1| 1 0 0 0 0 0 0 0 |
+ +-----------------+
+   A B C D E F G H
+```
+
 ### Counting Bit Sets
 
 https://graphics.stanford.edu/%7Eseander/bithacks.html#CountBitsSetParallel