In C is a musical piece composed by Terry Riley in 1964. It consists of series of 53 short melodic fragments that can be repeated at the discretion of the musicians. It is often cited as the first minimalist composition to make a significant impact on the public consciousness and inspire a new movement. The number of performers is unspecified. Riley suggests "a group of about 35 is desired if possible but smaller or larger groups will work".

The piece was premiered on November 4 and 6 1964, by Riley, Steve Reich, Jon Gibson, Pauline Oliveros, Stuart Dempster, Morton Subotnick and others at the San Francisco Tape Music Center. It received its first recorded release in 1968 on Columbia Records, where the full score for the piece was included on the sleeve.

In C was inspired by Riley's previous work with tape loops and delay, as well by his interest in group improvisation which he has been developing since 1957-58, alongside his fellow students Loren Rush and Pauline Oliveros. The piece has been recorded by a wide range of musicians, and went on to inspire many other minimalist composers like Philip Glass, Steve Reich, John Adams, Julius Eastman, etc.

In 2022, the 1968 LP recording of In C was selected by the Library of Congress for preservation in the United States National Recording Registry as being "culturally, historically, or aesthetically significant.".