By 1968 Al Kooper had played with Bob Dylan both on stage and in the studio, been a member of The Blues Project, and formed Blood, Sweat & Tears with Steve Katz (subsequently leaving after their first album). He was then working for Columbia Records as an A&R man.
In May 1968 he called up his old friend guitarist Mike Bloomfield and asked him to come to the studio to jam. Kooper and Bloomfield had worked together in 1965 on Bob Dylan's Highway 61 Revisited album. Bloomfield was curently working with his group The Electric Flag, but he was about to leave them. With Kooper on keyboards and Bloomfield on electric guitar, together with bassist Harvey Brooks (who had also worked with them on Highway 61 Revisited) and drummer Eddie Hoh they recorded a series of blues-based jams. Barry Goldberg also played electric piano on two of the numbers.
However Bloomfield was struggling with imsomnia and a heroin addiction - the next day, with more studio time booked, he failed to turn up. So Kooper called up Stephen Stills (who was then leaving Buffalo Springfield) to replace him on guitar.
The resultant album, Super Session, was credited on the cover to all three of them, the first side with Bloomfield and the second with Stills. Horn arrangements were afterwards added to some of the songs. The first side is firmly rooted in blues and is mostly instrumental, driven by Bloomfield's fantastic guitar playing. It's also notable for the nine-minute modal jazz-fusion number "His Holy Modal Majesty". The second side has more focus on Kooper's vocals, with renditions of Dylan's "It Takes A Lot To Laugh, It Takes A Train To Cry" (where Kooper plays 12-string guitar), Donovan's "Season Of The Witch" (which is drawn out into a fantastic 11 minute jam) and Willie Cobbs' "You Don't Love Me". Stills plays some brilliant lead guitar throughout.
Though it was initially conceived as just Al Kooper jamming with some of his famous musician pals, Super Session actually ended up becoming one of his best-known and most successful releases, and also known as featuring some of Bloomfield's best guitar playing.