Ars antiqua, also called ars veterum or ars vetus, refers to the music of Europe of the late Middle Ages between approximately 1170 and 1310, covering the period of the Notre Dame school of polyphony and the subsequent years which saw the early development of the motet. Usually the term is restricted to sacred music, excluding the secular song of the troubadours and trouvères; however sometimes the term is used more loosely to mean all European music of the thirteenth century and slightly before. The term ars antiqua is used in opposition to ars nova, which refers to the period of musical activity between approximately 1310 and 1375.

Almost all composers of the ars antiqua are anonymous. Léonin (fl. late 12th century) and Pérotin (fl. c.1180 – c.1220) were the two composers known by name from the Notre Dame school; in the subsequent period, Petrus de Cruce, a composer of motets, is one of the few whose name has been preserved.

In music theory the ars antiqua period saw several advances over previous practice, most of them in conception and notation of rhythm. The most famous music theorist of the first half of the 13th century, Johannes de Garlandia, was the author of the De Mensurabili Musica (about 1240), the treatise which defined and most completely elucidated the rhythmic modes. A German theorist of a slightly later period, Franco of Cologne, was the first to describe a system of notation in which differently shaped notes have entirely different rhythmic values (in the Ars cantus mensurabilis of approximately 1280), an innovation which had a massive impact on the subsequent history of European music. Most of the surviving notated music of the 13th century uses the rhythmic modes as defined by Garlandia.