Beyond the Door (Italian: Chi sei?, lit. "Who are you?") is a 1974 supernatural horror film directed by Ovidio G. Assonitis and Roberto Piazzoli, and starring Juliet Mills, Gabriele Lavia, and Richard Johnson. The plot follows a San Francisco housewife who becomes demonically possessed in the midst of a pregnancy. The film was a co-production between the United States and Italy. It was released in the United Kingdom in an extended cut under the title Devil Within Her.

Beyond the Door opened in the United States in May 1975, and became a major commercial success, grossing approximately $15 million. Critical reaction to the film was largely negative, with numerous critics deeming it an imitation of The Exorcist (1973). That film's distributor, Warner Bros., filed a lawsuit against the production company behind Beyond the Door, claiming copyright infringement. A settlement was ultimately reached years later in 1979.

This would be the first entry into the Beyond the Door trilogy in the United States as Mario Bava's Shock (1977) was re-titled Beyond the Door II and branded as a sequel, though it has no relation to the 1974 film. A second sequel, Beyond the Door III, was also released in 1989, though it too bears no relation to the previous two films.