In the Court of the Crimson King (subtitled An Observation by King Crimson) is the debut album from the English rock band King Crimson, released on 10 October 1969 on Island Records in England and Atlantic Records in America. The album is one of the first and most influential of the progressive rock genre, where the band largely departed from the blues influences that rock music was founded upon and combined elements of jazz, classical, and symphonic music.

The album reached No. 5 on the UK Albums Chart and No. 28 on the US Billboard 200, where it was certified Gold by the Recording Industry Association of America. The album was reissued several times in the 1980s and 1990s using inferior copies of the master tapes. After the masters were located in 2003, a 40th-anniversary edition of the album was released in 2009 with new stereo and 5.1 surround sound mixes by Steven Wilson