Founded in Amsterdam in 1967 by saxophonist Willem Breuker, pianist Misha Mengelberg, and percussionist Han Bennink, Instant Composers Pool (or ICP) was an independent free jazz label and orchestra that would go on to release over fifty albums featuring such pillars of the scene as Derek Bailey, Peter Brötzmann, Evan Parker, Jeanne Lee, John Tchicai, and Steve Lacy. Based around the concept that improvisation was, in fact, an act of instantaneous composition, ICP's legacy on improvised and free music is impossible to overstate.

A live performance from May of 1970 in Rotterdam, Groupcomposing features a North Sea-crossing ICP lineup of British free improv luminaries Derek Bailey on guitar, Evan Parker on saxophone, and Paul Rutherford on trombone, along with ICP mainstays Han Bennink, his brother Peter, Misha Mengelberg, and Peter Brötzmann. The first side, "Groupcomposing, Part 1" is a nearly all-out assault with the reeds trio and Rutherford's trombone blasting nigh-continuously for the album's first side, culminating in a blistering Peter Bennink bagpipes solo. "Part 2" acts at first as the comedown, beginning with a playful piano and percussion back-and-forth before meandering a dark, brooding, path of trill horns to the album's eventual, tense conclusion.

Recorded just a few years into the ICP's long tenure, it is hard to think of a release more representative of the label's musical principles – or, more broadly, of the power of free group improvisation – than the aptly-named Groupcomposing. This limited reissue marks the first time the album has been in print on vinyl in over forty years.