By the early '60s, Riley was regularly holding solo harmonium performances beginning at 10 p.m. and continuing until sunrise, an obvious precursor of the all-night underground raves to follow decades later. After graduating Berkeley in 1961, his next major work was 1963's Music for the Gift, composed for a play written by Ken Dewey; among the first pieces ever generated by a tape delay/feedback system, it employed two tape recorders -- a setup Riley dubbed the "Time Lag Accumulator" -- playing a loop of Chet Baker's rendition of Miles Davis' "So What." The loop effect sparked Riley's interest in repetition as a means of musical expression, and in 1964, he completed his most famous work, the minimalist breakthrough In C; a piece constructed from 53 separate patterns, it was a landmark composition that provided the conception for a new musical form assembled from interlocking repetitive figures.

In time, Riley also learned to play saxophone, introducing the instrument into his so-called all-night flights; these epic improvisational performances became the basis for his most successful recordings, 1968's Poppy Nogood and the Phantom Band, and the following year's A Rainbow in Curved Air, the music's cyclical patterns and ethereal atmospherics predating the rise of the ambient concept by several years. In 1970, Riley made the first of many trips to India to study under vocal master Pandit Pran Nath, with whom he frequently performed in the years to come; another collaborator was John Cale; that pairing resulted in the 1971 LP Church of Anthrax, arguably Riley's most widely known recording outside of experimental music circles. Throughout the '70s, he also taught composition and North Indian raga at Mills College in Oakland, California

A pair of early-'70s live performances -- one in L.A., the other in Paris -- resulted in the 1972 album Persian Surgery Dervishes, a work of meditative machine music clearly prescient of the trance sound to follow. Around the same time, while on staff at Mills, he befriended David Harrington of Kronos Quartet; the two collaborated on a number of concertos for string quartet and orchestra -- one even commissioned by the Salzburg Festival in 1991. Another Riley/Kronos collaboration, 1989's Salome Dances for Peace, was nominated for a Grammy. Recording less frequently as the years passed, Riley agreed to stage a performance celebrating the silver anniversary of In C, which was then released in 1990. Through the rest of the decade, and even into the 21st century, Riley saw his own works either re-released or had previously unissued early tapes released by various labels, including the Cortical Foundation, Wergo, and Elision Fields.

He didn't stop working, however. In 2001, Kronos Quartet released Terry Riley: Requiem for Adam on Nonesuch, and Riley issued Atlantis Nath on his own Sri Moonshine label. In 2005, he collaborated with poet Michael McClure on I Like Your Eyes Liberty (also on Sri Moonshine). Riley also worked with avant-garde bassist Stefano Scodanibbio on Diamond Fiddle Language, which was issued by Wergo the same year.

Riley turned 70 in 2008, and the year was marked by two releases. The first was the major Cusp of Magic by Kronos Quartet for Nonesuch. They had commissioned Riley to create a new work for them to celebrate the occasion of his birthday; the composer happily accepted. Later in the year, Riley released the more playful Banana Humberto on Sri Moonshine. He had the delightfully strange Autodreamographical Tales issued by Tzadik in 2010, on which he played all the instruments, and sang and recited stories and dream narratives. Riley released a live concert album with his son Gyan on Sri Moonshine in 2011, and followed it up with his two-hour, long-form composition Aleph for Korg Triton 88 synthesizer (originally created for the Aleph-Bet Sound Project at the Contemporary Jewish Museum in San Francisco); it was released by Tzadik in early 2012.