Big Fat Liar is a 2002 American teen comedy film directed by Shawn Levy, and written by Dan Schneider from a story by Schneider and Brian Robbins. It stars Frankie Muniz, Paul Giamatti and Amanda Bynes, with a supporting cast featuring Amanda Detmer, Donald Faison, Lee Majors and Russell Hornsby.

The plot, alluding to the Aesop's Fable, The Boy Who Cried Wolf, follows a 14-year-old compulsive liar (Muniz), whose creative writing assignment "Big Fat Liar" is stolen by an arrogant Hollywood producer (Giamatti), who later plans to use it to make the fictional film of the same name. It was released in the United States on February 8, 2002, to commercial success and mixed critical reviews. It was followed by a 2017 standalone direct-to-DVD critically panned sequel.