Chanson is a French word for song, and in English-language contexts is often applied to any song with French words, particularly a cabaret song. In a more specialised usage, it refers to a polyphonic French song of the late Middle Ages.
Early chansons tended to be in one of the formes fixes, ballade, rondeau or virelai, though some composers later set popular poetry in a variety of forms. The earliest chansons were for two, three or four voices, with first three becoming the norm, expanding to four voices by the 16th century. Sometimes, the singers were accompanied by instruments.
The first important composer of chansons was Guillaume de Machaut, with later figures in the genre including Johannes Ockeghem and Josquin Desprez. Guillaume Dufay and Gilles Binchois wrote so-called Burgundian chansons, which were somewhat simpler in style, while Claudin de Sermisy and Clément Janequin were composers of so-called Parisian chansons which abandoned the formes fixes (as Josquin had also done) and were in a simpler, more homophonic style (many of these Parisian works were published by Pierre Attaingnant). Later composers, such as Orlando de Lassus, were influenced by the Italian madrigal.
See also the early medieval heroic lays called Chansons de gestes, which were declaimed (from memory) rather than actually being sung.