OM formed in 2003 when former Sleep members Al Cisneros and Chris Hakius began to play again after a six year hiatus. The two began rehearsing without the addition of guitar or other instruments. OM's first three albums feature Cisneros (bass/vocals) and Hakius (drums). In January 2008 Hakius left the group. Cisneros recruited drummer Emil Amos and in March of 2008 OM recorded a 7" for Sub Pop records. The song "Gebel Barkal" is the first to feature Amos on drums. Cisneros and Amos are currently writing for the next Om full-length which is to be recorded in early 2009.

The band's live performances are of a devotional nature. Their 2007 concert in the city of Jerusalem spanned over five and a half hours. Cisneros' unmistakable chants address processes of mind, psychic reality, astral and causal planes of being, and the nature of the soul.

Om has played numerous international festivals, some of which are: All Tomorrow's Parties, Dour, Donau, Supersonic, Roadburn, Primavera, Festival International de Musique Actuelle de Victoriaville, Wire Adventures in Modern Music, ArthurBall, ArthurNights, Wall of Sound, Le Lieu Unique - Nantes, SXSW, X Avant, and No-Fi UK.