The Beast from 20,000 Fathoms is a 1953 American independent monster film directed by Eugène Lourié, with stop motion animation by Ray Harryhausen. It is partly based on Ray Bradbury's 1951 short story of the same name, which was later reprinted as "The Fog Horn". In the film, the Rhedosaurus, a giant dinosaur is released from its frozen state in the Arctic by an atomic bomb test. Paul Christian stars as Thomas Nesbitt, the foremost surviving witness of the creature before it causes havoc while traveling toward New York. Paula Raymond, Cecil Kellaway, and Kenneth Tobey are featured in supporting roles.

Jack Dietz and Hal E. Chester arranged the production of a monster movie in response to the successful 1952 re-release of King Kong (1933). While Lou Morheim and Fred Freiberger were solely credited for screenwriting, many contributed to writing the film, including Dietz, Harryhausen, and Lourié. On an estimated $210,000–285,000 budget, principal photography occurred in New York from July to August 1952, under the title The Monster from Beneath the Sea. Harryhausen and Willis Cook created the special effects over roughly six months. In 1953, Warner Bros. bought the film for $400,000–800,000, retitled it, and hired David Buttolph to replace Michel Michelet's original score.

The Beast from 20,000 Fathoms was released throughout the United States in June 1953, to widespread critical praise for its special effects. The film grossed over $5 million worldwide, making it one of the highest-grossing films of 1953. It pioneered the "atomic monster" genre and is credited with launching the giant monster and kaiju movie trend that ensured its initial release. Godzilla (1954) is often cited as having taken inspiration from the film. In recent years, The Beast from 20,000 Fathoms has acquired a cult following and has been listed among the greatest science fiction, horror, and B movies of the 1950s.