Olivier Messiaen’s teaching exerted a notable and formative influence on Pierre Boulez’s work as it matured from 1944 to 1946. Many historiographies of the twentieth century provide accounts of this relatively brief teacher-student relationship, as well as of Boulez’s subsequent turn away from Messiaen’s music. This chapter provides a chronology of their much more enduring relationship, based primarily on music analysis and historical data rather than on both composers’ often mythologised testimonies about each other. It surveys Boulez’s time of study with Messiaen, as well as the significance of Messiaen in Boulez’s account of his own role in the historical progress of music after the Second World War. Finally, discussion of Boulez’s artistic cooperation with the pianist Yvonne Loriod, Messiaen’s second wife, leads into a presentation of Boulez as an important champion of Messiaen’s orchestral music.