When Boulez returned to France in the mid 1970s, he assumed a number of significant roles in French cultural life, setting up IRCAM, forming the Ensemble Intercontemporain and assuming a professorship at the Collège de France. While undoubtedly a practical man, he was also interested in theorising about music and its relationship with the other arts, its place in culture and its philosophical underpinnings. The early years after his return to France brought him into the orbit of Roland Barthes, Gilles Deleuze and Michel Foucault, three of the most active intellectual figures in France of the 1970s and all four of them were to participate in the seminar Le Temps musical, which Boulez organised as an IRCAM event in 1978. This chapter considers Boulez’s contact with these three intellectuals, the seminar on musical time which brought them together and the small body of letters they exchanged in the years that followed.