The Practice of Socialist Internationalism examines the efforts of the British, French, and German socialist parties to cooperate with one another on concrete international issues. Drawing on archival research from twelve countries, it spans the years from the First World War to the early 1960s, paying particular attention to the two post-war periods, during which national and international politics were recast. In addition to highlighting a neglected dimension of twentieth-century European socialism, the volume provides novel perspectives on the history of internationalism and the history of international politics. By practicing internationalism, European socialists sought to forge a new practice of international relations, one that would emerge from their collective efforts to work out 'socialist' approaches to pressing issues of international politics such as post-war reconstruction, European integration, and decolonization.