Between May 1949 and August 1954 the composers Pierre Boulez and John Cage exchanged a series of remarkable letters which reflect on their own music and the music and culture of the time. This correspondence, together with a further letter from 1962 and various other relevant documents, have been edited by Jean-Jacques Nattiez and appear here for the first time completely in English. At the time Cage and Boulez were great friends and these amicable letters reflect their differing ideas on the course new music should take. While Boulez was thinking about forms of serialism, Cage was moving in the direction of ever greater compositional freedom and chance procedures. Professor Nattiez has written a full introduction to this collection of documents and the meticulous and detailed annotation of every letter makes this a volume of extraordinary value for our understanding of the development of both Cage and Boulez and the music of their time.