William "Billy" Baldwin (born February 21, 1963) is an American actor, known for his starring roles in such films as Backdraft (1991) and Flatliners (1990).

Baldwin was born in Massapequa, New York, the son of Carol Newcomb (née Martineau) and Alexander Rae Baldwin, Jr., a high school history/social studies teacher and football coach. He is the brother of notable actors Daniel, Stephen and Alec, sometimes collectively known as the Baldwin brothers. Baldwin was raised in a Catholic family of Irish, English and French descent. A graduate of Berner High School and Binghamton University, he has a degree in political science and is known for his support and contributions to Binghamton's wrestling team.

Before starting his acting career, he was a fashion model. Baldwin starred alongside Cindy Crawford in the 1995 film Fair Game, and has continued to act in films and on television, but he has not taken many leading roles. He was well-received in a supporting role in the 2005 film The Squid and the Whale. Currently, he co-stars as Donald Sutherland's oldest son, Patrick Darling IV, on Dirty Sexy Money, for ABC.