Pierre Boulez is a great force in contemporary music and is committed to the extension and reproduction of the musical language. This documentary looks at his work, notably the creation of Répons, which has been announced as the signal of a "new age of instrumental achievement" (Financial Times). Boulez rehearses in his Parisian New Music Lab (IRCAM). He talks about his experimentation, the difficulties of communicating his ideas, and the post-war composers who influenced him.