diff --git a/readme.txt b/readme.txt
index 3a31b0d..59fbb71 100644
--- a/readme.txt
+++ b/readme.txt
@@ -51,6 +51,11 @@ can defend the selected tile.  All three of these options basically give a
 visual representation of the Attack DB.  The colors are: For attackers Cyan
 and for defenders Red.
 
+Lastly, the game has an Undo/Redo stack that tracks the last 254 moves. Pressing
+u will undo the last move and r will redo the last move.  In an AI/Human game,
+the undo will undo the last AI and human player move, so the human player can
+make a different move.
+
 
 III.  Distribution