[4][5] Al Kooper and Mike Bloomfield had worked together on the sessions for Bob Dylan's ground-breaking classic Highway 61 Revisited, and played in the backing band for his controversial performance with electric instruments at the Newport Folk Festival in July 1965.

[6] Kooper booked two days of studio time at CBS Columbia Square in Los Angeles in May 1968, and recruited keyboardist Barry Goldberg and bassist Harvey Brooks, both members of the Electric Flag, along with well-known session drummer "Fast" Eddie Hoh.

On the second day, with the tapes ready to roll, Bloomfield returned to his home in Mill Valley in the San Francisco Bay Area, saying he had been unable to sleep.

[6] Needing to have something to show for the second day of booked studio time, Kooper hastily called upon Stephen Stills, who was in the process of leaving his band, Buffalo Springfield, to replace Bloomfield.

The success of the album opened the door for the "supergroup" concept of the late 1960s and 1970s, as exemplified by the likes of Blind Faith and Crosby, Stills & Nash.