Looney Tunes: Back in Action is a 2003 American live-action/animated comedy film produced and distributed by Warner Bros. Pictures. It is the second fully original theatrical feature film in the Looney Tunes franchise, and was directed by Joe Dante from a screenplay by Larry Doyle. The film stars Brendan Fraser, Jenna Elfman, and Steve Martin in lead roles, alongside Timothy Dalton, Joan Cusack, Heather Locklear, and Bill Goldberg in supporting roles, while Joe Alaskey leads the voice cast. Its plot, which parodies action and spy film conventions, follows Bugs Bunny and Daffy Duck (Alaskey) as they become intertwined in a plot by the ACME Chairman (Martin) to transform the world's population into subservient monkeys using the Blue Monkey diamond. They accompany aspiring stuntman DJ Drake (Fraser) and Warner Bros. executive Kate Houghton (Elfman) on their journey to thwart the Chairman's plot, which doubles as a mission to rescue the former's abducted father, Damian (Dalton).

The film was the result of multiple attempts by Warner Bros. to develop a sequel to Space Jam (1996). It was originally developed as a direct sequel titled Spy Jam, which was intended to include Jackie Chan in the lead role. Dante, out of a personal dislike for Space Jam, substantially developed the project to more closely represent the personalities of the Looney Tunes characters, with Walt Disney Animation Studios animator Eric Goldberg serving as the animation director. However, Dante reportedly had no creative control on the project, and the final film became different from what he intended. The film was the last project for composer Jerry Goldsmith, who died eight months following its release; John Debney composed additional material for the score.

Looney Tunes: Back in Action premiered on November 9, 2003, and was theatrically released in the United States on November 14. The film received polarizing reviews from critics who considered it an improvement over Space Jam and praised the animation and humor, but criticized the screenplay. It was a box office failure, grossing $68.5 million worldwide on an $80 million budget. Warner Bros., developing a franchise revival around the film, subsequently canceled several planned related projects, including new theatrical short films. It was the final film to be produced by Warner Bros. Feature Animation, and the last theatrical Looney Tunes feature film until Space Jam: A New Legacy in 2021.

At the 31st Annie Awards, the film was nominated for four Annie Awards, including Best Animated Feature.