When Olivier Messiaen (1908-1992) completed the vast opera Saint François d’Assise in 1983, he was mentally and physically exhausted, and believed that this monumental work would be his final compositional statement. In fact, he completed seven further works, 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 discernible 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. Part I of the book begins with a brief historical survey before discussing Saint François d’Assise as the work which defines everything that follows. Part II examines the series of miniatures that came after the opera and their links with Éclairs sur l’Au-Delà ..., his final masterpiece. Éclairs forms the subject of Part III of the book. Each movement is analysed in turn, before the work is considered as a whole and its hidden structure and motivic cohesion is revealed. Finally, Part IV considers the incomplete Concert à 4 and key stylistic features of the works of Messiaen’s final years.