Following his early appearances during the late 1940s and early 1950s as musical director of the Renaud-Barrault Theatre Company and the Domaine Musical, Boulez enjoyed a meteoric rise to prominence in the 1960s, becoming a conductor of international renown and securing prestigious posts with orchestras in London and New York. He also made waves in the opera house and pioneered seminal interpretations of works by Wagner, Debussy and Berg. Throughout his long career, he championed the music of the early modernist generation, much of which had been grievously neglected by other conductors, and also promoted key compositional figures of his own generation and a number of younger figures. This chapter explores Boulez’s development as a conductor in the context of his compositional activities and explains how his selfless commitment to the music he believed in changed the very nature of the conducting profession away from authoritarianism to a spirit of cooperation and collaboration.