When Olivier Messiaen (1908-1992) completed the vast opera Saint Francois d'Assise in 1983, he was mentally and physically exhausted, and believed that this monumental work would be his final compositional statement. Seven further works emerged, however, and these form the focus of the present study. Christopher Dingle suggests that, following the crisis provoked by the opera, Messiaen's music underwent a discernable change in style. He examines these seven works to identify characteristics of the composer's music, in particular an often overlooked aspect of his technique: harmony.