In these essays, the leading French composer and conductor Pierre Boulez explains many of his most significant ideas about music. The essays are divided into four parts, the first three concerned with common preoccupations (aesthetic, technical, and polemical) and the last a collection of entries intended for a music encyclopedia. Boulez offers penetrating and provocative analyses of the music of the major figures of twentieth-century music including Stravinsky, Schoenberg, Berg, Webern, Debussy, Messiaen, and Ravel. His illuminating comments arise from intimate knowledge of the music, and the resulting collection is an essential document of post-war modern music.