In his introduction to the score, Reich mentions that although the piece is named Music for 18 Musicians, it is not necessarily advisable to perform the piece with that few players due to the extensive doubling it requires. With only 18 musicians, the parts are divided as follows:
violin
cello
female voice
female voice
female voice
piano
piano
piano and maracas
marimba and maracas
marimba and xylophone
marimba and xylophone
marimba and xylophone
metallophone and piano
piano and marimba
marimba, xylophone, and piano
clarinet and bass clarinet
clarinet and bass clarinet
female voice and piano
The piece is based on a cycle of eleven chords. A small piece of music is based on each chord, and the piece returns to the original cycle at the end. The sections are named "Pulses", and Section I-XI.