Os Mutantes (Brazilian Portuguese: [uz muˈtɐ̃tʃis], The Mutants) are an influential Brazilian rock band that were linked with the Tropicália movement, a dissident musical movement during the Brazilian dictatorship of the late 1960s. The band is considered to be one of the main groups of Brazilian rock. Heavily influenced by Anglo-American psychedelic pop, they bridged Brazilian sensibilities together with studio trickery, feedback, distortion, and musique concrète. They released their now-acclaimed self-titled debut album in 1968.

Os Mutantes debuted their work in 1966, as a trio, when they presented themselves in the program O Pequeno Mundo de Ronnie Von of TV Record. The group was christened Mutantes by Ronnie Von himself, right before their first TV appearance. The group until then called themselves Os Bruxos (meaning The Witches, in Portuguese) and the suggestion came from the book Emperor of the Mutants, by Stefan Wul (the book's original title in French is La Mort Vivante). The group quickly became one of the main figures of the "new MPB" (popular Brazilian music), influenced by Tropicália, until their breakup in 1978, only with Sérgio Dias as an original member. Throughout these twelve years, nine albums were recorded, although two of them – O A e o Z and Tecnicolor – were only released in the 1990s. It was during this later decade that the importance of Os Mutantes was recognized, by both national and international rock, as one of the most creative dynamic, radical and talented groups of the psychedelic era.

Although the original line-up (Rita Lee, Arnaldo Baptista and Sérgio Dias; and later with Liminha and Dinho Leme) made the most notable breakthrough for the group, it has gone through numerous personnel changes throughout its existence. After a hiatus from the late 1970s to the early 2000s, the band reunited in 2006, touring and recording new material.