The Beast Within is a 1982 American supernatural horror film directed by Philippe Mora from a screenplay by Tom Holland, and starring Ronny Cox, Bibi Besch, Paul Clemens, and Don Gordon. Set in a small town in rural Mississippi, the story centers on a couple's son, who begins exhibiting strange behavior after his 17th birthday.

Producer Harvey Bernhard had purchased the rights to the then-unfinished novel based on the title alone. Due to the book not having been finished prior to production, the resulting script bears little resemblance to the source material. Principal photography officially began on February 8, 1981, in and around Jackson, Mississippi and concluded on April 10, 1981.

The Beast Within was released theatrically on February 12, 1982 by United Artists, and grossed a total of $7.7 million at the U.S. box office. The film drew criticism from film critics for its depictions of graphic violence and rape, as well as for its amalgamation of horror elements that numerous reviewers felt lacked cohesion; other critics, however, praised it for its tone and style, which was likened to that of the monster movies of the 1950s, as well as for its Southern Gothic atmosphere and themes, which drew comparison to the works of Tennessee Williams.