This dissertation studies the role of music in the twentieth-century French novel. It identifies a tension between Western classical music as a model of (social or aesthetic) harmony and the idea of notes taking sides. Novels take sides in debates about music and aesthetics, or explore the contested meanings of music in social/political contexts. I argue that music, as a social phenomenon, allows Romain Rolland (in Jean-Christophe [1904-1912]), Louis Aragon (in Les voyageurs de l’impériale [1942]) and Marguerite Duras (in Moderato cantabile [1958]) to deal with a whole host of social, cultural and political issues, as well as to seek new approaches to the novel at different moments in history. Each writer adopts a particular perspective on music as a site of both harmony and conflict: through the figure of the composer (Rolland), the character of the listener (Aragon), and through music as a formal model (Duras). Via a fictional composer, Rolland theorizes a music that can cross national boundaries, within a novel that—inspired by Wagner’s music—challenges the representational conventions of 19th-century naturalism. Aragon combines a realist representation of the social meanings of music and musical taste, with a social(ist) denunciation of bourgeois decadence and capitalism. While also depicting music’s entanglements with social class, Duras’ Moderato cantabile draws on two overlapping models of music that reflect the writer’s distinctive position within 1950s experimental literature. My study reveals a progressive shift away from the political potential of music toward an individual quest for transcendence—a tendency that will be continued in contemporary musical novels.