Messe de Nostre Dame (Mass of Our Lady) is a polyphonic mass composed before 1365 by French poet and composer Guillaume de Machaut (c. 1300–1377). It is one of the great masterpieces of medieval music and of all religious music; it is historically notable as the earliest complete setting of the Ordinary of the Mass attributable to a single composer, in contrast to earlier compilations such as the Tournai Mass.