William Joseph "Billy" Baldwin (born February 21, 1963) is an American actor, producer, and screenwriter, known for leading roles in films such as Flatliners (1990), Backdraft (1991), Sliver (1993), Fair Game (1995), Virus (1999), Double Bang (2001), as well as the role of Johnny 13 in Danny Phantom (2004–2007), The Italian Job (2004), Squid and the Whale (2005), Senator Patrick Darling in the ABC drama Dirty Sexy Money (2007–2009), Justice League: Crisis on Two Earths (2010), and was also a recurring guest on Gossip Girl as William van der Woodsen and on Parenthood as Gordon Flint. He also starred as Detective Brian Albert in the Lifetime original film The Craigslist Killer.

He is the brother of actors Alec Baldwin, Stephen Baldwin, and Daniel Baldwin. He is married to singer Chynna Phillips (Wilson Phillips), and they have three children.