Sunn O))) (pronounced "sun") is an American drone metal band from Seattle, Washington, that formed in 1998. The band is known for an extremely heavy sound that blends diverse genres including drone, black metal, dark ambient, and noise rock, and for very loud live performances. Supported by a varying cast of collaborators, the band was formed by two core members: Stephen O'Malley (also of Khanate and Burning Witch) and Greg Anderson (of Goatsnake and Engine Kid).

Sunn O))) is named after the Sunn amplifier brand, the logo of which includes a circle next to the "SUNN" banner with waves heading off to the right. In interviews, Stephen O'Malley stated that the band's moniker was also chosen as a play on the name Earth, a band widely regarded as pioneers of drone metal throughout the 1990s. Before the band members moved to Los Angeles, they briefly used the moniker Mars.

The band's style is characterized by extremely slow tempos, heavily distorted guitars, avoidance of rhythm and melody, and alternative tunings. The guitars are notable for their low register, frequently utilizing tunings as low as dropped A. Additionally, the band is known for using resonant feedback to create monolithic soundscapes and eerie atmospheres. Percussion is almost never incorporated, with a lack of any discernible beat. When performing live, the band wears robes, fills the air with fog, and plays at an extremely high volume.

The band releases the majority of its music through the label it founded in 1998, Southern Lord Records. However, the band initially released ØØ Void (its second album) on multiple labels, including Rise Above Records, Hydra Head Records, and Dirter Productions (which pressed it as a double album on vinyl). Additionally, the original pressing of The Grimmrobe Demos was released by Hydra Head Records. It was later issued as a double picture record set by Outlaw Recordings and finally reissued by Southern Lord in 2004.

Sunn O))) experiments with a variety of styles and sounds, progressing beyond the primarily guitar and bass style of The Grimmrobe Demos and ØØ Void. On White1 and White2, Sunn O))) noticeably expanded on conceptualization by inviting several guests (see collaborations below), resulting in everything from quiet meditative ambient sounds ("A Shaving of the Horn that Speared You" from White1) to a bizarre bass experiment track ("bassAliens" from White2). Black One continued in this direction, utilizing far more electronics, synthesizers, and other instrumentation than earlier Sunn O))) material, yet still marking a significant return to their traditional sound.

Sunn O))) are widely regarded as leaders in their genre, including by The New York Times Magazine of May 28, 2006, when the band was written up in an article called "Heady Metal" by John Wray[8]. The band was praised in an issue of Wonka Vision, an independent music magazine, as one of the greatest modern metal acts. Sunn O))) also appeared in the August 2007 issue of Q magazine (the "loud issue"), with its album White1 being named the 18th-loudest album of all time, just above AC/DCs Back in Black and below Jimi Hendrix's Are You Experienced?[ In 2008, Sunn O))) released a live album titled Dømkirke and also announced a mini-tour consisting of four concerts to commemorate the group's 10th anniversary, which coincided with the release of The Grimmrobe Demos.

The band's seventh studio album, Monoliths & Dimensions, was released on May 18, 2009, and was acclaimed by both press and public alike.

On December 17, 2009, the song "Hunting & Gathering (Cydonia)" from the CD Monoliths & Dimensions was named the Heaviest Song of All-Time by Jason Ellis on The Jason Ellis Show on Sirius/XM. Greg Anderson then appeared on The Jason Ellis Show on January 12, 2010.

The band played the ATP New York 2010 music festival in Monticello, New York, during September 2010, where it collaborated with Boris to perform the Altar album live.

For live performances, Hungarian-born Attila Csihar (Mayhem) has performed as the primary vocalist since 2003.

Sunn O))) released a collaboration album with Ulver titled Terrestrials in February 2014:[14] in October 2014, the band released the album Soused, a collaboration with singer-songwriter Scott Walker.[15] In November 2015, Sunn O))) presented a four-day program at Le Guess Who? Festival in Utrecht, the Netherlands, including Annette Peacock, Magma, Julia Holter and The Crazy World of Arthur Brown, and Sunn O))) itself.

Sunn O))) contributed to the original score of the horror film The Devil's Candy, which was released on March 17, 2017.

The band worked with producer Steve Albini on two albums, Life Metal (Released in April 2019) and Pyroclasts (Released in October 2019).