American Psycho is a 2000 American black comedy slasher film co-written and directed by Mary Harron, based on Bret Easton Ellis's 1991 novel of the same name. It stars Christian Bale, Willem Dafoe, Jared Leto, Josh Lucas, Chloë Sevigny, Samantha Mathis, Cara Seymour, Justin Theroux, Guinevere Turner, Reg E. Cathey and Reese Witherspoon.

Set in the 1980s, the film focuses on the actions of Patrick Bateman, the self-proclaimed "American psycho" of the title. While at first glance Bateman is a Yuppie New York City stockbroker, he is gradually revealed to be living a gruesome second life as a serial killer preying on prostitutes, work colleagues, and finally random members of the public.

Producer Edward R. Pressman purchased the film rights to the novel in 1992. After discussions with David Cronenberg fell through, Harron was brought on to direct and cast Bale in the lead role. Lionsgate acquired worldwide distribution in 1997 and temporarily replaced Harron and Bale with Oliver Stone as director and Leonardo DiCaprio portraying Patrick Bateman. DiCaprio left in favor of The Beach and Harron and Bale were brought back.

American Psycho debuted at the Sundance Film Festival on January 21, 2000, and was released theatrically on April 14, 2000. The film was a financial success and received generally positive reviews, with particular praise for both Bale's performance and the screenplay. It has since developed a cult following. A direct-to-video sequel, American Psycho 2, was released in 2002, albeit with almost no relation to the original.