He Knows You're Alone is a 1980 American slasher film directed by Armand Mastroianni, written by Scott Parker and starring Caitlin O'Heaney, Don Scardino, Elizabeth Kemp, Tom Rolfing, and Tom Hanks in his film debut. The plot follows a woman who is stalked by a killer targeting soon-to-be brides the weekend before her wedding.

Shot on location on Staten Island, New York, in late 1979, He Knows You're Alone was released theatrically in autumn 1980 by Metro-Goldwyn-Mayer and United Artists. Although the film received mostly negative reviews, it was a commercial success for MGM, grossing nearly $5 million at the US box office.

He Knows You're Alone has been credited for being one of the first horror films inspired by the success of Halloween, and shares a number of similarities with that previous hit.