Guillaume de Machaut (around 1300 - 1377), a French poet and composer, was a highly significant figure in the development of mediæval music and specifically in secular song (chanson).
Machaut was a priest and travelled extensively as the secretary of John, duke of Luxembourg. He was named as the canon of Rheims. His poetic output includes two large cycles, Le Remède de Fortune (The Cure of Ill Fortune) and Le Voir Dit (A True Story). Machaut's secular song output includes monophonic lais and virelais, which continue the tradition of the troubadors. However, his work in the polyphonic forms of the ballade and rondeau was more significant historically.
Machaut also wrote the first Mass which can be attributed to a single composer, his Messe de Notre Dame (Mass of Our Lady).