The International Refugee Organization (IRO) was founded on April 20, 1946 to deal with the massive refugee problem created by World War II. A Preparatory Commission began operations fourteen months previously. It was a United Nations specialized agency and took over many of the functions of the earlier United Nations Relief and Rehabilitation Administration. In 1952, its operations ceased, and it was replaced by the Office of the United Nations High Commissioner for Refugees (UNHCR).
The Constitution of the International Refugee Organization, adopted by the United Nations General Assembly on December 15, 1946, specified the agency's field of operations. Controversially, this defined "persons of German ethnic origin" who had been expelled, or were to be expelled from their countries of birth into the postwar Germany, as individuals who would "not be the concern of the Organization." This excluded from its purview a group that exceeded in number all the other European displaced persons put together. Also, because of disagreements between the Western allies and the Soviet Union, the IRO only worked in areas controlled by Western armies of occupation.
Eighteen countries acceeded to membership of the IRO: Australia, Belgium, Canada, China, Denmark, the Dominican Republic, France, Guatemala, Iceland, Italy, Luxembourg, the Netherlands, New Zealand, Norway, Switzerland, the United Kingdom, the United States, and Venezuela. The U.S. provided about 40% of the IRO's $155 million annual budget. The organisation's first Director General was William Hallam Tuck, succeeded by J. Donald Kingsley on July 31, 1949.