In C is a semi-aleatoric musical piece composed by Terry Riley in 1964 for any number of people, although he suggests "a group of about 35 is desired if possible but smaller or larger groups will work". It is a response to the abstract academic serialist techniques used by composers in the mid-twentieth century and is often cited as the first minimalist composition.

http://rapidshare.com/files/213735612/TerryRiley-InC.pdf