This dissertation investigates how German-language critics articulated and publicly negotiated ideas about music and expressionism in the first five years after World War I. A close reading of largely unexplored primary sources reveals that "musical expressionism" was originally conceived as an intrinsically musical matter rather than as a stylistic analog to expressionism in other art forms, and thus as especially relevant to purely instrumental rather than vocal and stage genres. By focusing on critical reception of an unlikely group of instrumental chamber works, I elucidate how the acts of performing, listening to, and evaluating "expressionist" music were enmeshed in the complexities of a politicized public concert life in the immediate postwar period. The opening chapters establish broad music-aesthetic and sociopolitical contexts for critics' postwar discussions of "musical expressionism." After the first, introductory chapter, Chapter 2 traces how art and literary critics came to position music as the most expressionist of the arts based on nineteenth-century ideas about the apparently unique ontology of music. Chapter 3 considers how this conception of expressionism led progressive-minded music critics to interpret expressionist music as the next step in the historical development of absolute music. These critics strategically—and controversially—portrayed Schoenberg's "atonal" polyphony as a legitimate revival of "linear" polyphony in fugues by Bach and late Beethoven. Chapter 4 then situates critical debates about the musical and cultural value of expressionism within broader struggles to construct narratives that would explain Germany's traumatic defeat in the Great War and abrupt restructuring as a fragile democratic republic. Against this backdrop, the later chapters explore critics' responses to public performances of specific "expressionist" chamber works. Chapter 5 traces reactions to a provocative performance of Schoenberg's Chamber Symphony, op. 9 (1906) at the Berlin Volksbühne in February 1920. Chapter 6 examines the interplay of musical-aesthetic and sociopolitical issues in critical reception of several postwar concerts that juxtaposed Schoenberg's "expressionist" Chamber Symphony with Franz Schreker's "impressionist" Chamber Symphony (1916). Chapter 7 considers how critics situated performances of Alexander Zemlinsky's Second String Quartet, op. 15 (1916) in relation to ideas about "expressionism" in music. Finally, Chapter 8 considers critical reception of performances of Béla Bartók's Second String Quartet, op. 17 (1917) in the context of two concert series sponsored by "expressionist" journals: the Anbruch-Abende in Vienna (1918) and the Melos-Abende in Berlin (1922 and 1923). Each of these final chapters uses contemporary criticism as a vehicle for a close reading of the relevant musical work, resulting in a portrait of "expressionist" music that is both contextually and musically nuanced.