The Dunwich Horror is a 1970 American supernatural horror film directed by Daniel Haller, and starring Sandra Dee, Dean Stockwell, and Ed Begley. A loose adaptation of the short story of the same name by H.P. Lovecraft, the film concerns a young female graduate student who is targeted by a man attempting to use her in an occult ritual taken from the Necronomicon. The screenplay was co-written by Curtis Hanson, while Roger Corman served as an executive producer on the film.

The film's distributor, American International Pictures, had tentatively planned an adaptation of the Lovecraft story in 1963. Executive producer Corman hired Haller to direct, as he had previously directed several features for him, including Devil's Angels (1967). Though set in the fictional Massachusetts town of Arkham, principal photography of The Dunwich Horror took place in and around Mendocino, California in the spring of 1969. The film marked Sandra Dee's first adult role, following the break in her contract with Universal Pictures, and she envisioned the picture as a major departure from the films she had appeared in as a child and teen actor, in which she had been presented in a very wholesome way.

The Dunwich Horror premiered in Chicago in January 1970, and screened throughout the country that year, as well as internationally. Critical response was divided, with some critics praising the film's technical elements and adaptation of the source material, while others felt the performances were ineffective, and the film generally mediocre. Despite this, some contemporary film scholars, such as Alain Silver, have championed it as one of the best film adaptations of a Lovecraft literary work. Film historian Rob Craig similarly deemed it "one of the most overall successful adaptations of a Lovecraft source work ever committed to film." Aesthetically, the film has been noted for its psychedelic posterized imagery.