An American Werewolf in London is a 1981 horror film written and directed by John Landis. An international co-production of the United Kingdom and the United States, the film stars David Naughton, Jenny Agutter, Griffin Dunne and John Woodvine. The title is a cross between An American in Paris and Werewolf of London. The film's plot follows two American backpackers, David and Jack, who are attacked by a werewolf while travelling in England, causing David to become a werewolf under the next full moon.

Landis wrote the first draft of the screenplay for the film in 1969 and shelved it for over a decade. Prospective financiers believed that Landis's script was too frightening to be a comedy film and too humorous to be a horror film. After achieving success in Hollywood with the comedies The Kentucky Fried Movie, National Lampoon's Animal House and The Blues Brothers, Landis was able to secure financing from PolyGram Pictures to produce An American Werewolf in London.

An American Werewolf in London was released in the US by Universal Pictures on August 21, 1981. It was a critical and commercial success, winning the 1981 Saturn Award for Best Horror Film and makeup artist Rick Baker winning the inaugural Academy Award for Best Makeup. Since its release, it has become a cult classic. A sequel, An American Werewolf in Paris, was released by Hollywood Pictures in 1997.