This dissertation studies the representations of crowds, their marginalized figures and paradigmatic types in Irish and British fiction from the fin de siecle to the mid-twentieth century. "Crowded Margins" anatomizes twentieth-century fictional crowds as they act in counterpoint with established imagined communities such as nation, shared history and language, and compares literary crowds to models operating in the realms of political, psychoanalytic and social theory. The project demonstrates the centrality of collective experience to modernist style, analyzes how modernist fictional representations of crowds intervene in theorizations of agency, identity and operation, and draws new connections between aesthetic productions and political change during the period. It shows that a considerable number of the period's literary texts anticipate postmodernity's anti-totalizing identities, and current academic work on the political multitude, such as what has been produced about the multitude's mobility or its discursive indeterminability, in empire studies and theories of biopolitics. "Crowded Margins" proposes a fresh account of collective autonomy and efficacy by positing that in these literary texts the crowd recognizes itself as a diasporic and agile network which supervises its own world-making and negotiates its cultural exchanges.