Undertow is Tool's first full-length album, released in 1993. When this album was released, grunge music was at its most popular, and pop punk was slowly beginning to become popular. Undertow helped heavy metal music continue as a leading 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.
The album was recorded between October and December 1992 at Grand Master Studios, Hollywood, California, and includes songs that the band decided to not release on their previous EP, Opiate.