Guillaume de Machaut (sometimes spelled Machault) (c. 1300 – April 1377) is a Medieval French poet and composer.

He is one of the earliest composers on whom significant biographical information is available.

Well into the 15th century, Machaut's poetry was greatly admired and imitated by other poets, including Geoffrey Chaucer.

Machaut composes in a wide range of styles and forms.

He is a part of the musical movement known as the ars nova.

Machaut helps develop the motet and secular song forms (particularly the lai and the formes fixes: rondeau, virelai and ballade).

Machaut writes the Messe de Nostre Dame, the earliest known complete setting of the Ordinary of the Mass attributable to a single composer.