Colosseum are an English jazz rock band, mixing blues, rock and jazz-based improvisation. Colin Larkin wrote that "the commercial acceptance of jazz rock in the UK" was mainly due to the band. Between 1975 and 1978 a separate band Colosseum II existed playing progressive rock, founded by Colosseum band leader Jon Hiseman.

Colosseum, one of the first bands to fuse jazz, rock and blues, were formed in early 1968 by drummer Jon Hiseman and tenor sax player Dick Heckstall-Smith, who had previously worked together in the New Jazz Orchestra and in The Graham Bond Organisation, where Hiseman had replaced Ginger Baker in 1966. They met up again early in 1968 when they both played in John Mayall's Bluesbreakers, during which time they played on the Bare Wires album. Childhood friend Dave Greenslade was quickly recruited on organ, as was bass player Tony Reeves who had also known both Hiseman and Greenslade since being teenage musicians in South East London. The band's line-up was completed, after lengthy auditions, by Jim Roche on guitar and James Litherland (guitar and vocals), although Roche only recorded one track before departing.

Their first album, Those Who Are About to Die Salute You, which opened with the Bond composition "Walkin' in the Park", was released by Philips' Fontana label in early 1969. In March the same year they were invited to take part in Supershow, a two-day filmed jam session, along with Modern Jazz Quartet, Led Zeppelin, Jack Bruce, Roland Kirk Quartet, Eric Clapton, Stephen Stills, and Juicy Lucy.

Colosseum's second album, later in 1969, was Valentyne Suite, notable as the first release on Philips' newly launched Vertigo label, established to sign and develop artists that did not fit the main Philips brand, and the first label to sign heavy metal pioneers Black Sabbath.

For the third album, The Grass Is Greener, released only in the United States in 1970, Dave "Clem" Clempson replaced James Litherland. Louis Cennamo then briefly replaced Tony Reeves on bass, but was himself replaced by Mark Clarke within a month. Hiseman then recruited vocalist Chris Farlowe to allow Clempson to concentrate on guitar. This line-up had already partly recorded the 1970 album Daughter of Time.

In March 1971, the band recorded concerts at the Big Apple Club in Brighton and at Manchester University. Hiseman was impressed with the atmosphere at the Manchester show, and the band returned five days later for a free concert that was also recorded. The recordings were released as a live double album Colosseum Live in 1971. In October 1971 the original band broke up.

After the band split, Jon Hiseman formed Tempest with bassist Mark Clarke; Dave Greenslade formed Greenslade together with Tony Reeves; Chris Farlowe joined Atomic Rooster and Dick Heckstall-Smith embarked on a solo career. Clem Clempson joined the hit group Humble Pie.

Hiseman formed another group called Colosseum II in 1975, with a stronger orientation towards jazz-fusion rock. The band featured guitarist Gary Moore and Don Airey on keyboards. They released three albums before disbanding in 1978.