Ghidorah, the Three-Headed Monster (Japanese: 三大怪獣 地球最大の決戦, Hepburn: San Daikaijū Chikyū Saidai no Kessen, lit. Three Giant Monsters: Earth's Greatest Battle) is a 1964 Japanese kaiju film directed by Ishirō Honda, with special effects by Eiji Tsuburaya. Produced and distributed by Toho Co., Ltd., it is the fifth film in the Godzilla franchise, and was the second Godzilla film produced that year, after Mothra vs. Godzilla. The film stars Yosuke Natsuki, Hiroshi Koizumi, Akiko Wakabayashi, with Haruo Nakajima as Godzilla, Masanori Shinohara as Rodan, and Shoichi Hirose as King Ghidorah. In the film, an extraterrestrial from Venus, possessing the body of a princess, warns humanity of the pending destruction by the alien-dragon Ghidorah, with Godzilla, Rodan, and Mothra being their last hope for survival.

The film was rushed into production in order to replace Red Beard, which fell behind schedule, in Toho's New Year's holiday slate. The Godzilla suit and Mothra larva prop were recycled from the previous film, with modifications added, while new suits were produced for Rodan and Ghidorah, the latter creating on-set difficulties due to multiple wires attached to the suit. Principal photography began and ended in 1964 in Mount Aso, Yokohama, Gotenba, and Ueno Park.

Ghidorah, the Three-Headed Monster was theatrically released in Japan on December 20, 1964, followed by a theatrical release in the United States on September 29, 1965, by Continental Distributing as Ghidrah, the Three-Headed Monster. It earned ¥375 million (over $1 million) at the Japanese box office and $1.3 million at the American box office. The film received generally positive reviews from early and contemporary American critics.

The film was followed by the sixth film in the Godzilla franchise Invasion of Astro-Monster, released on December 19, 1965.