Captain Beyond is unique among predominately guitar driven hard rock albums in the fact that it contains a wide range of rock, heavy metal, and jazz influences often with various time signatures and broad range of dynamics (music) within the same song. The first five songs are composed in a fairly straight forward manner but the remainder of the album consists of two "suites" of tightly arranged interconnected songs; the first starting with "Thousand Days of Yesterdays (Intro)" and ending with "Thousand Days of Yesterdays (Time Since Come and Gone)" The second starts with "I Can't Feel Nothin' (Part 1)" and finishes the album. Songs flow directly into each other without benefit of any lag time between selections, a feature that is shared with other more progressive bands of the era such as Moody Blues, and Jethro Tull.
All of the songwriting was initially credited to Rod Evans and Bobby Caldwell; however, according to drummer Bobby Caldwell from a 2010 interview, all the songs were written and arranged by Evans, Reinhardt, himself and with some input from Dorman. Due to their still binding contracts at the time with Iron Butterfly Reinhardt and Dorman could not be listed as song writers on this record for legal reasons.