Blue Cheer was an American rock band that initially performed and recorded in the late 1960s and early 1970s and was sporadically active until 2009. Based in San Francisco, Blue Cheer played in a psychedelic blues rock or acid rock style. They are also credited as being some of the earliest pioneers of heavy metal, with their cover of "Summertime Blues" sometimes cited as the first in the genre. They have also been noted as influential in the development of genres as disparate as stoner rock, experimental rock, and grunge.

Blue Cheer was formed in 1966 by Dickie Peterson. Peterson had previously been with the Davis-based band the Oxford Circle along with future Blue Cheer members Paul Whaley and Gary Lee Yoder. The original Blue Cheer personnel were singer/bassist Peterson, guitarist Leigh Stephens and Eric Albronda as drummer. Albronda was later replaced by Whaley, who was joined by Peterson's brother Jerre (guitar), Vale Hamanaka (keyboards), and Jere Whiting (vocals, harmonica). Albronda continued his association with Blue Cheer as a member of Blue Cheer management, as well as being the producer or co-producer of five Blue Cheer albums.

The band was managed by Allen "Gut" Terk, a former member of the Hells Angels. Early on, it was decided that the line-up should be trimmed down. It has been said that Blue Cheer decided to adopt a power trio configuration after seeing Jimi Hendrix perform at the Monterey Pop Festival. The Who performed a live version of "Summertime Blues" at the same festival. Hamanaka and Whiting were asked to leave. Jerre Peterson did not want to remain in the group without them, so he departed as well, leaving Peterson, Stephens and Whaley as a trio.

Their first hit was a cover version of Eddie Cochran's "Summertime Blues" from their debut album Vincebus Eruptum (1968). The single peaked at No. 14 on the Billboard Hot 100 chart, their only such hit, and the album peaked at No. 11 on the Billboard 200 chart. In Canada, the song peaked at No. 3 on the RPM Magazine chart.

The "Summertime Blues" single was backed with Dickie Peterson's original song "Out Of Focus". Peterson also contributed to the album the eight-minute "Doctor Please" and "Second Time Around", which features Paul Whaley's frantic drum solo. Filling out the record, the band cranked out blues covers "Rock Me Baby" (by B.B. King) and "Parchman Farm" (Mose Allison, but retitled "Parchment Farm").

The group underwent several personnel changes, the first occurring after the 1968 release of Outsideinside after Leigh Stephens – who never used drugs – was asked to leave the band after criticizing his bandmates' behaviour. He was replaced by Randy Holden, formerly of Los Angeles garage rock band the Other Half. On 1969's New! Improved! there were different guitarists on side 1 and side 2 (Randy Holden and Bruce Stephens) due to Holden's unanticipated departure from the band. Following Holden's departure the band's line-up initially consisted of Dickie Peterson (bass), Tom Weisser (guitar), and Mitch Mitchell (drums), before Whaley returned and Bruce Stephens joined the band. Later, Ralph Burns Kellogg joined the band on keyboards. Blue Cheer's style now changed to a more commercial hard rock sound à la Steppenwolf or Iron Butterfly. By the fourth album, Blue Cheer, Paul Whaley had left the band and had been replaced by Norman Mayell, and following the release of the fourth album Bruce Stephens also left the band and was succeeded by Gary Lee Yoder who helped complete the album.

According to Peterson, the group's lifestyle during this period caused problems with the music industry and press. Peterson said the group was outraged by the Vietnam War and society in general.

The new line-up of Peterson, Kellogg, Mayell and Yoder in 1970 saw the release of The Original Human Being, followed by 1971's Oh! Pleasant Hope. When the latter album failed to dent the sales charts, Blue Cheer temporarily split up in 1971.