Rock ’n’ roll continued to evolve at a rapid pace throughout the '60s. By 1968, FM radio was emerging as a perfect outlet for rock musicians and fans tired of the limitations of the three-minute hit single. Album Oriented Rock (AOR), as a format, was still loose and free and always in need of new albums to fill the time. When these studio sessions took place, Al Kooper had just served up the Child Is Father to the Man–era Blood Sweat & Tears, Mike Bloomfield had been working with Electric Flag, and Stephen Stills was done with Buffalo Springfield and nearly signed up for Crosby, Stills & Nash. This set features expressive jamming on originals and covers. Though this landmark album is credited to the three of them, they never all play together. The first part consists of five tracks and features Kooper and Bloomfield, while the second "side" is tracks six through nine and features Kooper and Stills. The backing band features bassist Harvey Brooks and drummer Eddie Hoh. Subsequent reissues include Mike Bloomfield on the outtake “Blues for Nothing” and the live “Fat Grey Cloud” from the Fillmore West.