Mastermind is a 1976 Japanese-American comedy thriller film directed by Alex March and starring Zero Mostel, Keiko Kishi and Gawn Grainger. Filmed in 1969, it sat on the shelf for seven years before receiving a limited theatrical release in 1976. It has developed a cult following since its release on home video.

The second of producer Malcolm Stuart's two-picture deal with screenwriter, William Peter Blatty, the project was inspired by the success of the 1964 Peter Sellers comedy A Shot in the Dark which Blatty had co-written with producer/director Blake Edwards. Blatty's script was drastically revised by Ian McLellan Hunter prior to production, and the disgruntled screenwriter chose the pseudonym Terence Clyne for his screen credit. By 1973 it had recorded a loss of $2.9 million. Blatty's original screenplay was published as part of a limited edition collection by Lonely Road Books in 2013 as Five Lost Screenplays by William Peter Blatty.