Godzilla vs. Hedorah (Japanese: ゴジラ対ヘドラ, Hepburn: Gojira tai Hedora) is a 1971 Japanese kaiju film directed and co-written by Yoshimitsu Banno, with special effects by Teruyoshi Nakano. Produced and distributed by Toho Co., Ltd., it is the 11th film in the Godzilla franchise and Banno's directorial debut. The ensemble cast includes Akira Yamauchi, Toshio Shiba, Hiroyuki Kawase, Keiko Mari, and Toshie Kimura, with Haruo Nakajima as Godzilla and Kenpachiro Satsuma as Hedorah. The film features an environmentalist message as symbolized by Hedorah being spawned from pollution. It was released in the United States as Godzilla vs. the Smog Monster.

Producer Tomoyuki Tanaka offered Banno the opportunity to direct a Godzilla film shortly after working together on the Mitsubishi Pavilion at Expo '70. Franchise veterans Kaoru Mabuchi and Ishirō Honda were tasked with assisting Banno with scripting and directing the film respectively. Tanaka was hospitalized for the majority of the production, and Banno took advantage of this to include a scene he thought Tanaka would have otherwise rejected. Principal photography took 35 days with a crew of around 50 on an estimated ¥100 million budget.

Godzilla vs. Hedorah was distributed in Japan on July 24, 1971, as part of the Toho Champion Festival. It was a moderate box office success, grossing ¥290–300 million, and largely ignored by Japanese critics. The few contemporary reviews were generally unfavorable and conflicted about the scene where Godzilla uses his atomic breath to fly.

Godzilla vs. Hedorah is now considered a cult classic and has often been described as the most "unique" film in the Godzilla franchise. Retrospective critical reviews have been mixed to positive. Roger Ebert, Adam Wingard, and Nicolas Cage have hailed the film as their favorite in the Godzilla series. Banno proposed numerous follow-ups until he died in 2017. Although none of his submissions have ever come to fruition, one ultimately led to the production of Godzilla (2014), for which he served as an executive producer. A short based on the film premiered at Godzilla Fest 2021 in celebration of the film's 50th anniversary.

The film was followed by Jun Fukuda's Godzilla vs. Gigan, released on March 12, 1972,