Under Siege is a 1992 action thriller film directed by Andrew Davis from a screenplay 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.