Beginning with Debussy, the author traces growing freedom in the use of tonality and the different paths this emancipation took. Central to the book are the achievements of Schoenberg, Bartók, Stravinsky, and an insistence on the important role of jazz. Webern, Hindemith, and Prokofiev are also seen as important and seminal figures. The ramifications of their achievements and the individual contributions of many other composers born before 1910 are fully treated. Biographical information is given in so far as it throws light on the music. Many music examples offering representative passages, or even whole works, are analyzed. For readers who wish to pursue any aspect of the subject further, there is a comprehensive and annotated bibliography.