The Adventures of Buckaroo Banzai Across the 8th Dimension, often shortened to Buckaroo Banzai, is a 1984 American adventure science fiction comedy film produced and directed by W. D. Richter and written by Earl Mac Rauch. It stars Peter Weller in the title role, with Ellen Barkin, John Lithgow, Jeff Goldblum, and Christopher Lloyd. The supporting cast includes Lewis Smith, Rosalind Cash, Clancy Brown, Pepe Serna, Robert Ito, Vincent Schiavelli, Dan Hedaya, Jonathan Banks, John Ashton, Carl Lumbly and Ronald Lacey.

The film centers upon the efforts of the polymath Dr. Buckaroo Banzai, a physicist, neurosurgeon, test pilot, and rock star, to save the world by defeating a band of inter-dimensional aliens called Red Lectroids from Planet 10. The film is a cross between the action-adventure and science fiction film genres and also includes elements of comedy and romance.

After screenwriter W. D. Richter hired novelist Earl Mac Rauch to develop a screenplay of Mac Rauch's new character, Buckaroo Banzai, Richter teamed with producer Neil Canton to pitch the script to MGM/UA studio chief David Begelman, who took it to 20th Century Fox to make the film. Box office figures were low and less than half of the film's production costs were recovered. Some critics were put off by the complicated plot, although Pauline Kael enjoyed the film and Vincent Canby called it "pure, nutty fun." Buckaroo Banzai has been adapted for books, comics, and a video game and has attracted a loyal cult following.