<p> This dissertation examines the aesthetics of the mid-20th century musical avant-garde from an Arendtian perspective. I focus on three musical figures: Glenn Gould, Karlheinz Stockhausen, and Helmut Lachenmann. Each of these figures worked through the legacy of musical structuralism by staging various encounters with aspects of musical performance. My reevaluation of these musical figures is oriented by a reading of the contemporaneous political theories of Hannah Arendt, as found in <i>The Human Condition, On Revolution,</i> and <i> Between Past and Future,</i> in particular. In these Cold War era texts, Arendt argues that human cultures are constituted through the exemplary actions of individuals, who risk their lives for the sake of communal principles, thereby imprinting these contestable societal norms upon public consciousness. </p><p> Arendt&rsquo;s account of action, revolution and political judgment have much in common with a broader performative turn that was taking place in avant-garde artistic practices of the same time (c. 1950 &ndash; 1970). This turn resituated the ontology of the musical work from the notated page to the physical acts and technologies of sound production. Of deeper provenance, however, is the fact that Arendt&rsquo;s political theories have an important basis in her appropriation of Kantian aesthetics. I argue that the Kantian inspired elisions of politics and art in her theory justifies re-mapping her political concepts onto art. I refer to these re-mappings as inversions to draw attention to the pivotal role that performance plays in Arendt&rsquo;s theories, operating as a hinge between political and aesthetic categories. I do so also to ground a material history of the encounters with musical formalism that took place in the creative practices of my musical subjects. Thus my title, <i>Action Aesthetics,</i> refers to this attempt to re-infuse Arendt&rsquo;s political theory of exemplary action into the modernist musical legacy of Kantian aesthetics.</p><p>