A Perfect Circle (APC) is an alternative rock supergroup formed by guitarist Billy Howerdel and Tool frontman Maynard James Keenan. The original incarnation of the band also included Paz Lenchantin on bass, Troy Van Leeuwen on guitar, and Tim Alexander on drums. The latest line-up features Marilyn Manson bassist and former Nine Inch Nails bassist Jeordie White, former guitarist for The Smashing Pumpkins, James Iha, and session drummer Josh Freese, who is most well known for his work with Nine Inch Nails and The Vandals. Despite having a varied cast since inception, the stylistic content of the songs has remained consistent with Howerdel as composer, and Keenan penning the lyrics.

A Perfect Circle has released three albums: Mer de Noms, Thirteenth Step and Emotive. A CD-DVD set, Amotion, has also been released and contains thirteen music videos in addition to a number of song remixes created by Danny Lohner. The group has not recorded, toured or released any new material since its hiatus began in 2004. Since then band members have worked on other projects; the most notable being Keenan's work on Tool's 2006 album 10,000 Days, and Howerdel's founding of the band Ashes Divide.

In a recent interview, Keenan announced that he and Howerdel have been working on new material, officially ending the group's hiatus. The extent to which Iha, White, and Freese will be involved is unknown.

Mer de Noms (1999–2001)

A Perfect Circle was conceived by Billy Howerdel, a former guitar technician for Nine Inch Nails, The Smashing Pumpkins, Fishbone and Tool. Howerdel met singer Maynard James Keenan in 1992 when Fishbone was opening for Tool, and the two became friends. Three years later, Keenan offered Howerdel, who was looking for lodging, a room in his North Hollywood home. This provided Howerdel the opportunity to play demos of his music for Keenan. Pleased with what he heard, Keenan remarked, "I can hear myself singing songs." Although he originally desired a female vocalist, Howerdel agreed that Keenan would be a good fit, and A Perfect Circle was formed a short time later. They were then joined by bassist and violinist Paz Lenchantin, former Failure guitarist Troy Van Leeuwen, and the previous drummer for Primus, Tim Alexander. The band played their first show at LA's Viper Club Reception on August 15, 1999. After playing shows in L.A., the band entered the studio to begin work on their first album. Alexander was soon replaced with session drummer and member of The Vandals, Josh Freese, but Alexander's performance can still be heard on the album version of the song "The Hollow".

The band's debut album, Mer de Noms (French for "Sea of Names"), was released on May 23, 2000. Howerdel had been working on some of the music, including tracks "Hollow" and "Breña", as far back as 1988. Soon after recording for the album was finished, the band began touring. Initially, they served as the opening act for Nine Inch Nails on the 2000 Fragility v2.0 tour, but they then embarked on a number of headlining tours all over the world, including the Canadian festival, Summersault. As Keenan was well known through his other band, he would often wear long wigs on his otherwise bald head when performing, to distinguish himself from his Tool persona. Mer de Noms was released on October 31, 2000, while the band was on tour. The album is distinctive in that it is the highest ever debut for a new rock band, selling over 188,000 copies in its first week, and appearing at number four on the Billboard 200.