An English progressive rock/jazz fusion band from the Canterbury Scene consisting of Phil Manzanera (guitars), Bill MacCormick (bass), Dave Jarrett (keyboards) and Charles Hayward (drums).

Having originated from a college band by the name of Pooh and the Ostrich Feather, Quiet Sun was formed in 1970 after MacCormick had made friends with Robert Wyatt, the son of a friend of his mother. The band integrated jazz elements and sparkling keyboard sounds into their complex music - similar to Soft Machine - but Manzanera's energetic guitar made their music very different from the Softs who had not been using any guitar (other than bass guitar) on their regular albums before the 1975 release of Bundles, and had used reeds as the main other melody instruments aside of keyboards.

Quiet Sun split up in 1972, Manzanera to Roxy Music, MacCormick to Matching Mole, Hayward to This Heat and Jarrett began to teach mathematics.

In 1975, Manzanera booked a studio for 26 days to record his album Diamond Head and got Quiet Sun together again to record an album from their old composed material in the studio at the same time. This first and only album of theirs, with the participation of Brian Eno and the late Ian MacCormick, titled Mainstream was critically acclaimed.