The collapse of Nazi Germany was accompanied by a humanitarian disaster of staggering proportions. The newly-founded United Nations Relief and Rehabilitation Administration (UNRRA) and its successor the International Refugee Organization (IRO) identified repairing the damage that the war had inflicted on Allied displaced populations as one of its foremost humanitarian obligations. These UN agencies cast themselves as pre-eminent agents of ‘rehabilitation’, facilitating a fast transition from war to peace through scientific methods of refugee management conducted along Rooseveltian lines. Departing from earlier relief efforts, their ambition was to provide more than a mere ‘soup kitchen’ charity, their aim being to ‘rehabilitate’ Displaced Persons (DPs). Their methods were, however, vigorously contested in the field by military and occupation authorities, by members of established voluntary societies, and by UNRRA/IRO’s own continental recruits. This thesis explores these confrontations through the lens of French DP administration. Although these UN agencies proclaimed a new era of internationalism, solutions to DP problems were often defined in nationalist terms. DPs were organised by ethnicity and strong ties attached relief workers to their own national groups. For French planners and humanitarian workers, the DP question was much more than a humanitarian problem, and was bound up with issues of domestic reconstruction, culture and identity as much as the provision of medical aid and relief. This thesis demonstrates that distinctive diplomatic constraints, economic requirements and cultural differences influenced the thought and practices of refugee humanitarianism, shaping alternate ways of arranging interim provision and ‘rehabilitating’ DPs in the French zone of occupation. Despite the fact that Allied responses to the DP problem mirrored divergent wartime experiences and differing national visions for the post-war future, this thesis argues that the history of UNRRA and the IRO in the French zone cannot be solely understood as a story of inter-Allied confrontation and clashes of political culture. Numerous transfers of expertise and the circulation of ideas and people between the zones belie such a view. New-Deal influenced methods penetrated the French zone and local UNRRA/IRO staff progressively embraced the organizations’ declared mission of ‘self-help’, albeit on terms that reflected their particular interpretation of DPs’ best interests. The real impact of UNRRA and the IRO lies in this grey area of subtle processes of imitation and re-interpretation.