Deep Blue Sea is a 1999 American science fiction horror film directed by Renny Harlin. It stars Saffron Burrows, Thomas Jane, Samuel L. Jackson, Michael Rapaport, and LL Cool J. It is the first film of the film series of the same name. Set in an isolated underwater facility, the film follows a team of scientists and their research on mako sharks to help fight Alzheimer's disease. The situation plunges into chaos when multiple genetically engineered sharks go on a rampage and flood the facility.

Deep Blue Sea had a production budget of $60 million and represented a test for Harlin, who had not made a commercially successful film since Cliffhanger in 1993. The film was primarily shot at Fox Baja Studios in Rosarito, Mexico, where the production team constructed sets above the large water tanks that had been built for James Cameron's 1997 film Titanic. Although Deep Blue Sea features some shots of real sharks, most of the sharks used in the film were either animatronic or computer generated. Trevor Rabin composed the film score; LL Cool J contributed two songs to the film: "Deepest Bluest (Shark's Fin)" and "Say What".

Released in theaters on July 28, 1999, Deep Blue Sea grossed $165 million worldwide. It received generally mixed reviews from critics, who praised its suspense, pacing, and action sequences, but criticized its unoriginality and B movie conventions. Retrospectively, Deep Blue Sea has been regarded as a successful shark film, especially within a limited genre that has been dominated by Steven Spielberg's 1975 thriller Jaws. Two direct-to-video sequels have been released: Deep Blue Sea 2 in 2018 and Deep Blue Sea 3 in 2020.