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). Widely regarded as one of the 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).