The fourteenth-century Ars Nova was one of the most significant movements of advance in musical history, and Guillaume de Machaut -- musician, poet, and priest -- was its greatest composer. This study of his music reflects the recent revival of interest in medieval music and elucidates for the modern reader the musical conventions of which it was created. Musicologist and medieval music pioneer Gilbert Reaney was born in 1924 in Sheffield, the son of a keen amateur musician. He read French and music at the city"s university, where, in 1951, he took his MA with a dissertation on the songs of the 14th-century composer Guillaume de Machaut. This followed army war service, where he had always been happy to contribute to camp concerts - "Corporal Reaney will now perform the Warsaw Concerto!" Back in Sheffield, Reaney developed a keen interest in medieval music and was soon editing manuscripts in this country and all over Europe. The founder of the London Medieval Group, he gave lecture recitals both here and abroad, and broadcast talks on what was then the BBC Third Programme. After holding research posts at Birmingham and Reading universities (1953-59), he was, for many years, a professor at UCLA (1961-97), where his fine pianism and wide-ranging repertoire were much appreciated. In due course he became editor of Musica Disciplina, while continuing to make numerous contributions to international conferences and other learned publications, not least on the subject of his beloved Machaut. He was a very modest man and a loyal friend. He never married, explaining that no wife would want a husband so constantly away from home.