Guillaume de Machaut, fourteenth-century French composer and poet, wrote the first polyphonic Mass and many other important musical works. Friend of royalty, prelates, noted poets, and musicians, Machaut was a cosmopolitan presence in late medieval Europe. He also served as canon of the cathedral of Reims, the coronation site of French kings. From this penetrating study of his music, Machaut emerges as a composer deeply involved in the great crises of his day, one who skillfully and artfully expressed profound themes of human existence in ardent music and poetry.