Walter H. Breen (September 5, 1928 – April 28, 1993) was an American author. He is best known among coin collectors for writing Walter Breen's Complete Encyclopedia of U.S. and Colonial Coins. "Breen numbers", from his encyclopedia, are widely used to attribute varieties of coins. He is also well known for activity in the science fiction fan community; and for his writings in defense of pederasty.