The French composer Olivier Messiaen (1908 - 92) is a musician about whom most remains to be discovered. More than a decade after his death our knowledge of Messiaen is largely conditioned by what he said about himself - in lectures and interviews, in his work as a teacher, and in the monumental seven-volume treatise that encompassed the whole of his composing world. But Messiaen's public documents conceal as much as they reveal, seldom explaining why a work was written, or what complexities went into its making. Almost nothing has been known about Messiaen's working practices. Indeed, the composer became fanatically secretive about any work in progress, and was similarly reticent about his private life. This is the first book to explore the world that Messiaen was at pains to keep hidden. It has been made possible by the unprecedented access to Messiaen's private archive granted to the authors by the composer's widow, Yvonne Loriod-Messiaen. The archive includes musical sketches, correspondence, lecture notes, diaries, as well as hundreds of photographs, many of which are published here for the first time. Using this remarkable material, Hill and Simeone trace the origins of many of Messiaen's greatest works, and place them in the context of his life, from his years at the Paris Conservatoire, his passionate first marriage to Claire Delbos, through to the immense achievements of his final decades.