This in-depth study explores the work of one of medieval music's most important figures, and in so doing presents an extended panorama of musical life in Europe at the end of the Middle Ages. Guillaume Du Fay rose from obscure beginnings to become the most significant composer of the fifteenth century, a man courted by kings and opes, and this study of his life and career provides a detailed examination of his entire output, including a number of newly discovered works. As well as offering musical analysis, this study investigates his close association with the Cathedral of Cambrai, and explores how, at a time when music was becoming increasingly professionalized, Du Fay forged his own identity as "a composer."