Undertow is the debut full-length album by American progressive metal band Tool, released in 1993. At the time, grunge was at the height of its popularity, and pop punk was slowly beginning to gather mainstream attention. Undertow helped heavy metal music remain prominent as a mainstream musical style, and allowed several later bands to break through to the mainstream. Allmusic saw the album's success in the "striking, haunting visuals that complemented the album's nihilistic yet wistful mood." It was eventually certified double platinum by the RIAA on May 14, 2001. As of July, 7, 2010, Undertow has sold 2,910,000 Copies in the US.
The album was recorded between October and December 1992 at Grand Master Studios, Hollywood, California, by Sylvia Massy. Some of the songs featured on the album are songs that the band decided to not release on their first EP Opiate.