Tracks 1-5 were previously released on singles in 1967 prior to the release of Days of Future Passed. They are the first Moody Blues releases to feature Justin Hayward and John Lodge.
Track 6, "A Simple Game", was later recorded by the Four Tops and (as "Simple Game"), went to #3 in the UK charts in 1972.
Tracks 7-11 formed the "+5" portion of the 1977 Caught Live + 5 album.
Track 12, "Late Lament," which rounds out the album, is the Graeme Edge poem that appears at the end of Days of Future Passed.
Though many of these tracks have also appeared on other releases, such as the Time Traveller box set and the 2006 SACD album remasters, Prelude is the only release that contains all eleven rarities.