This unique transnational history explores the extraordinary lives of left-wing volunteers who fought in not just one, but multiple conflicts across the globe during the mid-twentieth century.Utilising previously unpublished archival material, Heiberg, Acciai and Bjerström follow these individual soldiers through military conflicts that were, in most cases, geographically centred on individual countries but nonetheless evinced a crucial transnational dimension.From the Spanish Civil war of 1936 to the Nicaraguan Revolution of 1979, the authors marshall these diverse case studies to create a conceptual framework through which to better understand the networks and recruitment patterns of transnational volunteering.They argue that the Spanish Civil War created a model for this transnational left-wing military volunteering and that this experience shaped the global left responses to a range of conflicts throughout the twentieth century.