The Notre Dame school or the Notre Dame School of Polyphony refers to the group of composers working at or near the Notre Dame Cathedral in Paris from about 1160 to 1250, along with the music they produced.
The only composers whose names have come down to us from this time are Léonin and Pérotin. Both were mentioned by an anonymous English student, known as Anonymous IV, who was either working or studying at Notre Dame later in the 13th century. In addition to naming the two composers as "the best composers of organum," and specifying that they compiled the big book of organum known as the Magnus Liber Organi, he provides a few tantalizing bits of information on the music and the principles involved in its composition. Pérotin is the first composer of organum quadruplum — four-voice polyphony — at least the first composer whose music has survived, since complete survivals of notated music from this time are scarce.