Colombo Plan, international economic organization created in a cooperative attempt to strengthen the economic and social development of the nations of Southeast Asia and the Pacific. Officially the Colombo Plan for Cooperative Economic Development in Asia and the Pacific, it came into force in 1951 as the Colombo Plan for Cooperative Economic Development in South and Southeast Asia. There are 24 members and one provisional member, Mongolia. The original formulators of the plan were a group of seven Commonwealth nations; presently Australia, Japan, New Zealand, and the United States are the largest donors. Assistance is given in the form of educational and health aid, training programs, loans, food supplies, equipment, and technical aid; arrangements for assistance are made directly between a donor and a recipient country. Originally conceived as lasting for a period of six years, the Colombo Plan was extended several times until 1980, when it was extended indefinitely. The organization's headquarters are in Colombo, Sri Lanka.