Polyphony is music in which two or more independent melodic lines sound simultaneously, each preserving its own identity.
Polyphony emerged in Western music around the 9th century with early organum — a chant melody sung against a parallel line at a fixed interval — and developed through the Notre-Dame school of Léonin and Pérotin in 12th-century Paris. The 14th-century Ars Nova of Guillaume de Machaut and the 15th- and 16th-century Franco-Flemish masters — Dufay, Josquin, Ockeghem, Lassus, Palestrina — brought polyphony to extraordinary refinement. A Palestrina motet weaves four to six independent voices into shimmering coherence. Bach's fugues are the supreme later flowering. Polyphony is distinct from homophony (one melody supported by chords) and from monophony (single line). It demands more of the listener: rather than following one tune, you must hear several at once, each in its own time, all converging into a structure that no single voice could produce.