United Nations Relief and Rehabilitation Administration (UNRRA) was an international relief agency, largely dominated by the United States but representing 44 nations. Founded in November 1943, it was dissolved in September 1948. it became part of the United Nations in 1945. Its purpose was to "plan, co-ordinate, administer or arrange for the administration of measures for the relief of victims of war in any area under the control of any of the United Nations through the provision of food, fuel, clothing, shelter and other basic necessities, medical and other essential services". Its staff of civil servants included 12,000 people, with headquarters in New York. Funding came from many nations, and totalled $3.7 billion, of which the United States contributed $2.7 billion; Britain, $625 million; and Canada, $139 million.

UNRRA cooperated closely with dozens of volunteer charitable organizations, who sent hundreds of their own staff to work alongside UNRRA. In operation for only four years, the agency distributed about $4 billion worth of goods, food, medicine, tools, and farm implements at a time of severe global shortages and worldwide transportation difficulties. The recipient nations had been especially hard hit by starvation, dislocation, and political chaos. It played a major role in helping Displaced Persons return to their home countries in Europe in 1945–46.

Many of its functions were transferred to several UN agencies, including the International Refugee Organization and the World Health Organization. As an American relief project, it was later replaced by the Marshall Plan, which began operations in 1948. However, the historian Jessica Reinisch has shown that UNRRA should not just figure as a chapter in U.S. history. UNRRA's uniqueness was that it managed to bring together very different partners and models of international relief, each of which had their own history and antecedents.