In the Court of the Crimson King

Recorded at Wessex Sound Studios in London on a one-inch eight-channel machine, with Robin Thompson engineering and Tony Page assisting. The band first tried the album with Tony Clarke producing, at Morgan Studios in June and again at Wessex in July 1969. On 16 July they walked away. Their managers arranged for the 15,000 pound recording cost to be guaranteed, and their own sessions began at Wessex on 21 July. In about three days they laid down backing tracks, with a day each for I Talk to the Wind and Epitaph, a day for Moonchild, and 21st Century Schizoid Man done in one live take. August went on mixing down to two tracks to make room for overdubs.

McDonald overdubbed layers of Mellotron and woodwinds, in some cases through five tape generations. On Epitaph he mixed two separate Mellotron parts against each other, which he said gave the sustained chords a "sense of motion". The cover is a painting by Barry Godber, a friend of Sinfield, who used his own face seen in a mirror. Fripp said the face on the outside is the Schizoid Man and the one inside is the Crimson King.

The album reached five on the UK chart and 28 on the Billboard 200, where it was certified Gold. NME's Nick Logan called it "totally original and always captivating". Rolling Stone's John Morthland said the band had combined many forms "to create a surreal work of force and originality". Edward Macan wrote in 1997 that it "may be the most influential progressive rock album ever released". Reviewing the 2019 anniversary set, Pitchfork's Ryan Reed called the album "a towering pillar of musicianship, wonder, and menace". Rolling Stone ranked it second on its 2015 list of the 50 greatest prog rock albums, behind The Dark Side of the Moon. The 2019 box added an alternate Schizoid Man built on a June 1969 backing track from the abandoned Morgan session, and a mostly a cappella Epitaph.