An American composer associated with the minimalist school.

Born in Colfax, California, Riley studied at Shasta College, San Francisco State University and the San Francisco Conservatory before earning an MA in composition at the University of California, Berkeley, studying with Seymour Shifrin and Robert Erickson. He was involved in the experimental San Francisco Tape Music Center working with Morton Subotnick, Steve Reich, Pauline Oliveros and Ramon Sender. His most influential teacher, however, was Pandit Pran Nath, a master of Indian classical voice who also taught La Monte Young and Marian Zazeela. Riley made numerous trips to India over the course of their association to study and to accompany him on tabla, tambura and voice. Throughout the 1960s he travelled frequently around Europe as well, taking in musical influences and supporting himself by playing in piano bars, until he joined the Mills College faculty in 1971 to teach Indian classical music.

Also during the 1960s were the famous All-Night Concerts, during which Riley performed mostly improvised music from evening until sunrise, using an old organ harmonium and tape-delayed saxophone. When he finally wanted a break, after hours of playing, he played back looped saxophone fragments recorded throughout the evening.

Riley began his long-lasting association with the Kronos Quartet after meeting its founder, David Harrington, while at Mills. Over the course of his career Riley has composed 13 string quartets for the ensemble, in addition to other works. He wrote his first orchestral piece, Jade Palace, in 1991, and has continued to pursue that avenue, with several commissioned orchestral compositions following. Riley is also currently performing and teaching both as an Indian raga vocalist and as a solo pianist.

While his early endeavours were influenced by Stockhausen, Riley changed direction after first encountering La Monte Young, in whose Theater of Eternal Music he later performed from 1965-66. Riley has stated that it was Young's ideas that were at the heart of minimalism, although more composers have come to name Riley himself as an influence. The String Quartet (1960) was Riley's first work in this new style. It was followed shortly after by a string trio, in which he first employed the repetitive short phrases that he (and minimalism) are now known for.

His music is usually based on improvising through a series of modal figures of different lengths, such as in In C and the Keyboard Studies. In C (1964) is probably Riley's best-known work and one that brought the minimalist music movement to prominence. Its first performance was given by Steve Reich, Jon Gibson, Pauline Oliveros and Morton Subotnick, among others, and it has influenced their work and that of many others, including John Adams and Philip Glass. Its form was an innovation: the piece consists of 53 separate modules of roughly one measure apiece, each containing a different musical pattern but each, as the title implies, in C. One performer beats a steady stream of Cs on the piano to keep tempo. The others, in any number and on any instrument, perform these musical modules following a few loose guidelines, with the different musical modules interlocking in various ways as time goes on. The Keyboard Studies are a single-performer version of the same concept.

This format, with a collection of minimal musical elements coming together to form a complex and cohesive whole, launched a movement that was a step away from the increasing academicism in western classical music. The complex formal structures of the Second Viennese School and the neoclassicists had dominated the classical musical landscape throughout the middle of the 20th century; the minimalistic movement abandoned that formalism. Riley often further denied strict structure by introducing improvisational elements into his compositions (although he had long been improvising in solo performance). One of the primary pieces to use this approach was his A Rainbow In Curved Air (1968). This work and Poppy Nogood and the Phantom Band, its companion piece on a recording issued in 1969, were intended to give a necessarily truncated impression of the sound of Riley's all-night concerts.

For a time Riley stopped notating his works at all, focussing on Indian classical music and solo performance. Working with the Kronos Quartet has led him back to more structured, notated music, but improvisatory elements remain an important part even of the works composed for them.

Being on the leading edge of music was nothing new for Riley. Already in the 1950s he was working with tape loops, a technology then in its infancy, and he has continued manipulating tapes to musical effect, both in the studio and in live performance, throughout his career. He has composed in just intonation as well as microtonal pieces.

Other collaborators include the Rova Saxophone Quartet. He has also had a notable collaboration with Beat poet Michael McClure, with whom he has released several albums and most recently contributed music to a London revival of his play The Beard.

A Rainbow In Curved Air inspired Pete Townshend's synthesizer parts on the Who's Won't Get Fooled Again and Baba O'Riley, the latter apparently named in tribute to Riley as well as to Meher Baba.