Ars subtilior is a musical style characterized by rhythmic and notational complexity, centered on Paris, Avignon in southern France, and also in northern Spain at the end of the fourteenth century. The style also is found in the French Cypriot repertory. Often the term is used in contrast with ars nova, which applies to the musical style of the preceding period from about 1310 to about 1370; though some scholars prefer to consider ars subtilior a subcategory of the earlier style. Primary sources for ars subtilior are the Chantilly Codex, the Modena Codex, and the Turin Manuscript.

Ars nova refers to a musical style which flourished in the Kingdom of France and its surroundings during the Late Middle Ages. More particularly, it refers to the period between the preparation of the Roman de Fauvel (1310s) and the death of composer Guillaume de Machaut in 1377. The term is sometimes used more generally to refer to all European polyphonic music of the fourteenth century. For instance, the term "Italian ars nova" is sometimes used to denote the music of Francesco Landini and his compatriots, although Trecento music is the more common term for the contemporary 14th-century music in Italy. The "ars" in "ars nova" can be read as "technique", or "style". The term was first used in two musical treatises, titled Ars novae musicae by Johannes de Muris, and a collection of writings attributed to Philippe de Vitry often simply called "Ars nova" today. Musicologist Johannes Wolf first applied to the term as description of an entire era in 1904.