This monograph is an authoritative study of the oeuvre of one of the most important composers of our time. For the first time, Ligeti's key works are presented in the context of their drafts and sketches. His personal and artistic development is set forth and illuminated, and his principal compositions are analyzed and reinterpreted, based on detailed studies of the scores and drafts, as well as on personal conversations with the composer. In addition, numerous questions concerning today's composing are raised and discussed. Music does not have to be puristic: Ligeti's spheres of interest are close to universal, embracing history, natural science, and visual arts, as well as music of diverse eras and ethnicities. This expanded world of the musical comprises not just tones and sounds, speech and music, the vocal and the instrumental: Ligeti conceives music as a cosmos of acoustic form.