The Notre-Dame school, also called the Notre-Dame school of polyphony, is a group of composers who worked near the Notre-Dame Cathedral in Paris between about 1160 and 1250. These composers created music that used multiple voices singing together.

Only two composers from this time are known by name: Léonin and Pérotin. An anonymous English student, known as Anonymous IV, wrote about them in the late 1200s. He called them "the best composers of organum" and mentioned they created a large collection of organum music called the Magnus Liber Organi. He also shared some details about how their music was written and performed. Pérotin is known for writing the first surviving example of organum quadruplum, which is music with four separate voices singing together.

Léonin, Pérotin, and other unnamed composers whose music has survived are part of a period in European music history called the ars antiqua. During this time, the motet—a type of musical piece—was first developed from a section of music called the clausula, which appears often in the Magnus Liber Organi.

Although many written musical scores from this time have survived, how the music was played, especially the rhythm, is still debated. Three music theorists—Johannes de Garlandia, Franco of Cologne, and Anonymous IV—described the practices of the time. However, they wrote more than two generations after the music was created, and their descriptions might reflect how music was played later, not how it was originally intended. In many pieces from the Notre-Dame School, the lowest voices sing long notes, while the higher voices sing more complex, decorated lines with repeating patterns of long and short notes called "rhythmic modes." This marked the start of musical notation that could show how long different notes should be played.

Notre-Dame motets

Bevilacqua states, "It is known that Parisian organum and related musical styles were being developed in the last quarter of the twelfth century. However, no written collection dating before the 1230s has been found. The surviving Notre-Dame sources do not date earlier than the 1230–40 period." The earliest known motets are the Notre-Dame motets, composed by musicians such as Leonin and Perotin during the thirteenth century. These motets used multiple melodies sung simultaneously, with each voice containing a different text. They also used rhythmic modes, which are specific rhythmic patterns. An example is the motet Salve, salus hominum/O radians stella/nostrum by Perotin, written between 1180 and 1238. Nunes-Le Page and her colleagues note, "There are many uncertainties about the exact dates when polyphonic music first appeared. However, it is very likely that if Bishop Odo de Sully declared the use of polyphonic music for important religious ceremonies in decrees from 1198 and 1199, such music existed before those decrees."

Contemporary accounts

Polyphony allowed musicians to create music that some people found beautiful and others found unpleasant. John of Salisbury, a philosopher and bishop, taught at the University of Paris during the time Léonin was active, but before Pérotin. He often attended services at the Notre-Dame Choir School. In his book Policraticus, he described what was happening to music during the High Middle Ages.