Harry Partch (June 24, 1901 – September 3, 1974) was an American composer, music theorist, and creator of musical instruments. He composed using scales of unequal intervals in just intonation, and was one of the first 20th-century composers in the West to work systematically with microtonal scales. He built custom-made instruments in these tunings on which to play his compositions, and described his theory and practice in his book Genesis of a Music (1947).

The scales Partch composed with scales dividing the octave into 43 unequal tones derived from the natural harmonic series; these scales allowed for more tones of smaller intervals than in standard Western tuning, which uses twelve equal intervals to the octave. To play his music, Partch built a large number of unique instruments, with such names as the Chromelodeon, the Quadrangularis Reversum, and the Zymo-Xyl. Partch described his music as corporeal, and distinguished it from abstract music, which he perceived as the dominant trend in Western music since the time of Bach. His earliest compositions were small-scale pieces to be intoned to instrumental backing; his later works were large-scale, integrated theater productions in which he expected each of the performers to sing, dance, speak, and play instruments. Ancient Greek theatre and Japanese Noh and kabuki heavily influenced his music theatre.