The thesis is an analytical study of the structure and activities of the International Transport Workers' Federation(ITF) from 1945 to 1965.It gives particular attention to the nature of the ITF's memberships, especially its expansion to the United States and to the Third World; to the ITF's political stance in a period of enormous international tension and to the interrelationship of both those factors. The ITF was founded in 1896 and there are few substantial transport workers' unions which are not yet affiliated. It has long been recognized as the most effective of all the international trade union organizations. The ITF made a significant contribution to the Allied war effort in the Second World War and its membership in every branch of the international transport industry took on great strategic importance during the Cold War. The thesis is based on original research, making special use of the ITF's extensive archives at the Modern Records Centre of the University of Warwick. There is a close and critical focus on the ITFs political engagement, exemplified by its controversial part in countering communist influence in European ports in the early 1950s at the time of the introduction of the European Recovery Programme (the Marshall Plan). This discussion is, however, set in the context of the ITF's structures and its broader social and industrial concerns, such as the defence of trade union and civil rights and assistance to transport workers' unions in the newly de-colonized developing countries. The conclusions draw out the main findings of the research and discuss the dearth of academic literature on the international trade union movement, and especially the almost total neglect of 'International Trade Secretariats', organizations such as the ITF which group together national trade unions in specific industries and services. On this basis, it surveys a poorly served theoretical field and outlines implications for future theoretical analysis.