The People's Republic of Letters sketches a media history of socialist internationalism. Such a history is bound to be partial because of the multiplicity of media---print, music, theater, film, and others---that sustained a worldwide socialist culture in the twentieth century. While devoting most of its attention to the engage novel, which occupied a central place in leftist cultural thought for much of that century, this dissertation also examines two other media forms that have superseded it as the main source of publics co-terminous with the worldwide left: singer-songwriter performance of the 1960s (or guitar poetry, as I shall call it) and political documentary film today. Not unlike the nineteenth-century novel and newspaper in Benedict Anderson's famous account, all three served as technologies of the imagined community of the international left. They not only helped sustain its unity and resolve its multiple contradictions but also gave it its distinctive affective horizons and cemented the historical bloc between the left's main constituents: the intellectuals and the working classes.These cultural forms fulfilled these functions in one of two ways: (1) by the act of circulating and providing common texts to leftists from different parts of the world or (2) by inscribing leftist communities into their narratives and imagining the solidarities that bound them. This dissertation applies both of these approaches to each of the media under consideration. The concept of a (counter-)public helps us mediate between the two.Taking as its starting point the literary interactions of interwar readers and writers living in state socialism with their leftist counterparts outside, Part I of this dissertation questions the framework of Soviet manipulation of foreign sympathizers, which has characterized much of the earlier scholarship on those interactions, and goes on to conceptualize them as constitutive of a proper international literary field, with agents, institutions, borders, and principles of operation. That field I shall call the People's Republic of Letters. The Old-Left novel, with its apostolic narratives of conversion, persecution, martyrdom, and community, provided its lifeblood. As the case of the mid-twentieth-century American proletarian novelist Howard Fast suggests, the Soviet state was both the condition of possibility for the People's Republic and the reason for its demise. In-between, it could never quite control the Republic.While Western leftist writers and readers like Fast were withdrawing from the People's Republic, it was attracting new ones from the emerging Third World. Part II of this dissertation reconstructs this attempt of a common Soviet-Afro-Asian literary front between the late 1950s and the late 1970s and examines the alignment of separate national struggles into a broader international project inscribed into many Third-World novels.As a whole, however, in the second half of the twentieth century, the novel was losing its capacity to construct political publics. Guitar poetry assumed that role with respect to the 1960s social movements in Eastern and Western Europe, North and South America. Part III of this dissertation is devoted to the spontaneous, non-hierarchical, and carnivalesque character of its homologous national publics, which, like the movements they expressed, rarely succeeded in linking up internationally.This dissertation will end with a reflection on the contemporary political documentary film as the main medium common to contemporary leftists worldwide.