This album featured the only track to be written by all five members of the band. The opening "Procession" was a piece that was intended to describe the history of music from the beginning of time up until the album's recording. The only three words heard in this track – "desolation," "creation," and "communication" – were similarly used (along with many other "-ation" words) in "One More Time to Live."
The album reached #1 on the British album charts, in addition to a three-week stay at #2 in the United States, and produced one top-40 single, "The Story in Your Eyes." The track "Emily's Song" was written by John Lodge for his newborn daughter. Mike Pinder wrote and sang the album's concluding track "My Song".
The title is taken from the student mnemonic for the lines of the treble clef: E-G-B-D-F. These notes are heard played on piano during "Procession."
The album was the last to feature the Mellotron as the sole tape-driven instrument, as it would be utilized in conjunction with the Chamberlin (another device that uses recorded tape to generate sound) on the Moody Blues' next studio album, 1972's Seventh Sojourn. The album was mixed and released in both stereo and quadraphonic. In April 2007 the album was remastered into SACD format and repackaged with the two extra tracks.
In 2008 a remaster for standard audio CD was issued with the same bonus tracks.
The front cover has been imitated by the leader of the dark progressive band Current 93, David Tibet, for Halo, a live album released in 2004.