Gamera, the Giant Monster (大怪獣ガメラ, Daikaijū Gamera) is a 1965 Japanese kaiju film directed by Noriaki Yuasa, with special effects by Yonesaburo Tsukiji. Produced and distributed by Daiei Film, it is the first film in the Gamera franchise and the Shōwa era. The film stars Eiji Funakoshi, Harumi Kiritachi, and Junichiro Yamashita. In the film, authorities deal with the attacks of Gamera, a giant prehistoric turtle unleashed in the Arctic by an atomic bomb.

The success of The Birds and Toho's Godzilla films influenced studio head Masaichi Nagata to produce a similar film. In 1964, Daiei attempted to produce Nezura, with Yuasa directing. However, the project was shut down by the health department, since the project was to have used dozens of live rats. Nagata then conceived Gamera to replace Nezura on the schedule. Due to a low budget and tight schedule, Yuasa was forced to use outdated equipment, faulty props, and faced belittlement from colleagues. Yuasa was determined to complete the film with Daiei's resources, despite brief talks of hiring Tsuburaya Productions to finish the film.

Gamera, the Giant Monster was theatrically released in Japan on November 27, 1965. A localized version with new footage was theatrically released in the United States on December 15, 1966 by Harris Associates, Inc. and World Enterprises Corporation as Gammera the Invincible. It was the only Gamera film in the Shōwa era to be given a theatrical release in the United States. The film was followed by Gamera vs. Barugon, released on April 17, 1966.