The Keep is a 1983 supernatural horror film written and directed by Michael Mann and starring Scott Glenn, Gabriel Byrne, Jürgen Prochnow, Alberta Watson and Ian McKellen. Set in Romania during World War II, it follows a group of Nazi soldiers who unleash a malevolent supernatural force after setting up camp in an ancient stone fortress in the Carpathian Mountains. It is an adaptation of the 1981 novel of the same title by American writer F. Paul Wilson. The musical score was composed by Tangerine Dream.

Filmed in Wales and at Shepperton Studios during the autumn of 1982, The Keep suffered numerous post-production problems, mainly the death of special effects supervisor Wally Veevers before he completed his work on the film. The film was also subject to significant editing troubles, as Mann's original director's cut was 210 minutes long, which its distributor, Paramount Pictures, required be cut to 120 minutes. After test screenings of the 120-minute version received unfavorable audience responses, the film was truncated to its final 96-minute cut, which was released theatrically in December 1983.

Upon release, The Keep received mixed reviews from film critics, with many criticizing it for its unclear narrative, though it received some praise for its visual elements, while it performed poorly at the U.S. box office. Despite this, the film has gone on to develop a cult following in the years since its release.