This document provides an overview of 20th century music styles including Impressionism, Expressionism, and Avant-Garde music. It defines Impressionism as using a wide range of colors and rhythms to express subtle feelings. Claude Debussy was a leading Impressionist composer. Expressionism is characterized as subjective, dissonant, and reflecting intense emotions. Arnold Schoenberg was a pioneer of atonal Expressionist music. Avant-Garde music explores unique fusions and elements ahead of its time. The document also lists characteristics and examples of these 20th century music styles.