Mushroom are known for known for an ever-changing lineup of players and a great deal of improvisation in their live shows and recordings, and their revolving door of personnel and willingness to experiment have led to guest appearances by many of their influences, including Gong's Daevid Allen, Soft Machine's Kevin Ayers, and Cream lyricist Peter Brown, and their catalog is vast with varying bootleg recordings and live albums.

Inspired by early-'70s Miles Davis albums like Big Fun and mid-'70s King Crimson, drummer Pat Thomas pooled together some Bay Area musicians in November 1996. He had been recording and releasing some material as a singer/songwriter in Germany and planned to record a bunch of instrumental jams to use as sound clips between his songs. After playing one of the segments (a 20-minute piece that eventually became "The Reeperbahn") for a friend who owned the Belmondo label, Thomas was asked if the imprint could release it as a single. Rather than use his own moniker, Thomas (masquerading as Patrick O'Hearn) quickly invented the name Mushroom, based on the fact that one of the bandmembers used to sell psychedelic mushrooms, and then insisted that the song be released as a 12" rather than sacrifice its length. About six months later, The Reeperbahn LP came out, and Thomas decided to do some shows to promote the record and put his songwriting career on hold. Originally, the band that was formed for these gigs tried to duplicate the originally recorded material, but not long after they switched to improvising in order to adhere to the group's core element of spontaneity.

In 1997 they released Alive and in Full Bloom, a studio album taken from the same session as their first 12". After a few years of performing loose shows, in 1999 Thomas and company recorded a Neu!-influenced, rhythmic Krautrock album called Hydrogen Jukebox and the busier and more frenetic Analog Hi-Fi Surprise in the same session. The year 2000 rolled around, and they put out rough mixes titled Compared to What as a prequel to the new musical groove they were headed toward with 2001's Foxy Music, a funky, riff-heavy, Head Hunters-influenced record. That year, they recorded the disc Oh, But They're Weird & They're Wonderful (inspired by a line from "Benny and the Jets") from live originals and experimental bits remixed by producer Dipstick. For a change of pace, they teamed up with Gary Floyd to record a remake of Les McCann & Eddie Harris' "Compared to What," and because of a strong musical chemistry, they decided to make a full album with him, 2003's Mad Dogs and San Franciscans.

In 2004 the band recorded Glazed Popems, a conceptual two-disc set. Disc one, titled London, embodies European psych and acid folk, and disc two, Oakland, is filled with '70s funk and soul. In 2007, they teamed up with trumpet legend Eddie Gale to make their most overtly jazz-based album to date, titled Joint Happening, and also released Yesterday I Saw You Kissing Tiny Flowers, an album of mostly live material done in collaboration with Alison Faith Levy. Naked, Stoned, & Stabbed was released in 2010 on the band's 4 Zero Records through Royal Potato Family. It is an album of 12 original songs unabashedly inspired by some of Mushroom's heros, including Alice Coltrane, Davy Graham, Fela Kuti, Sandy Bull, and Brian Eno. In addition, there is a remake of Kevin Ayers' "Singing a Song in the Morning" with guest vocalist Sonya Hunter. ~ Jason Lymangrover