Isaac Liev Schreiber (born October 4, 1967) is an American actor, director, screenwriter, producer, and narrator. He became known during the late 1990s and early 2000s after appearing in several independent films, and later mainstream Hollywood films, including the first three Scream horror films (1996-2000), Ransom (1996), The Hurricane (1999), Kate & Leopold (2001), The Sum of All Fears (2002), The Manchurian Candidate (2004), The Omen (2006), Defiance (2008), X-Men Origins: Wolverine (2009), Taking Woodstock (2009), Salt (2010), Pawn Sacrifice (2014), Spotlight (2015), The 5th Wave (2016), and The French Dispatch (2021).

For his roles in television, he most notably portrayed the eponymous protagonist of the Showtime drama series Ray Donovan (2013–2020). The role has earned him five Golden Globe Award nominations and three Primetime Emmy Award nominations. He reprised the role in the television film Ray Donovan: The Movie (2022). He has lent his voice to animated films such as My Little Pony: The Movie (2017), Isle of Dogs, and Spider-Man: Into the Spider-Verse (both 2018). He also narrated the HBO series Hard Knocks, 24/7 and the HBO documentary Magic & Bird: A Courtship of Rivals, as well as various PBS programs.

He has performed in several Broadway productions. In 2005, he won the Tony Award for Best Featured Actor in a Play for his performance in the play Glengarry Glen Ross. That same year, he made his debut as a film director and writer with Everything Is Illuminated (2005), based on the 2002 novel of the same name.