Coleman's quartet, like Gerry Mulligan's, was unusual in that it did not employ a chordal instrument such as a piano or guitar. Each composition contains a brief thematic statement, then several minutes of free improvisation, followed by a repetition of the main theme. While this resembles the conventional head-solo-head structure of bebop, it abandons the use of chord structures. "The Shape of Jazz to Come" found Coleman and his quartet elaborating on the sound and themes he had been developing throughout his career.