Tool is an American rock band from Los Angeles, California. Formed in 1990, the group's line-up includes drummer Danny Carey, guitarist Adam Jones, and vocalist Maynard James Keenan. Since 1995, Justin Chancellor has been the band's bassist, replacing their original bassist Paul D'Amour. Tool has won three Grammy Awards, performed worldwide tours, and produced albums topping the charts in several countries.

The band emerged with a heavy metal sound on their first studio album, Undertow (1993), and later became a dominant act in the alternative metal movement with the release of their second album, Ænima, in 1996. Their efforts to unify musical experimentation, visual arts, and a message of personal evolution continued with Lateralus (2001) and the most recent album, 10,000 Days (2006), gaining the band critical acclaim and commercial success around the world.

Due to Tool's incorporation of visual arts and very long and complex releases, the band is generally described as a style-transcending act and part of progressive rock, psychedelic rock and art rock. The relationship between the band and today's music industry is ambivalent, at times marked by censorship and the band's insistence on privacy.