This document summarizes several 20th century composers and their contributions to different musical styles. It covers impressionist composers Claude Debussy and Maurice Ravel. Expressionist composers Arnold Schoenberg and Igor Stravinsky are discussed. Bela Bartok is presented as a composer of primitivism. Neo-classical composers Sergei Prokofiev and Francis Poulenc are also mentioned. The document also outlines avant-garde composers like George Gershwin, Leonard Bernstein, and Philip Glass, as well as pioneers of electronic music like Edgar Varese and Karlheinz Stockhausen, and the developer of chance music, John Cage.