Under Siege is a 1992 action thriller film directed by Andrew Davis and written by J. F. Lawton. It stars Steven Seagal (who also produced the film), Tommy Lee Jones, Gary Busey, and Erika Eleniak. Seagal plays Casey Ryback, a former Navy SEAL, who must fend off a group of mercenaries after they commandeer the U.S. Navy battleship Missouri.

Released on October 9, 1992, Under Siege was both a critical and commercial success, receiving two Academy Award nominations for sound production and grossing over $156.6 million at the global box office. It is often considered Steven Seagal's best film to date. It was followed in 1995 by a sequel, Under Siege 2: Dark Territory, which was not as well received.

Under Siege was the final film of actor Patrick O'Neal, before his death in 1994.