Admitted as the 100th member of the UN on 27 September 1961, Sierra Leone participates in ECA and all the nonregional specialized agencies. The country belongs to the African Development Bank, Commonwealth of Nations, ECOWAS, G-77, and AU. In 1980–81, President Siaka Stevens served as Chairman of the OAU, and Freetown hosted the organization's summit conference in July 1980; high-level ECA and ECOWAS meetings took place in Freetown in the following year. Sierra Leone is a member of the WTO and a signatory to the Lomé Convention and the Law of the Sea.
Sierra Leone signed a defense pact with Guinea in 1971 allowing for the exchange of some army personnel. In October 1973, Sierra Leone and Liberia concluded the Mano River Union agreement, aimed at establishing an economic union of the two countries; Guinea joined the union in 1980. Trade restrictions among the three nations were abolished in 1981, and a common external tariff was established for most items of trade. President Kabbah has participated in efforts to establish a West African Monetary Zone (WAMZ) that would include The Gambia, Ghana, Guinea, Liberia, Nigeria, and Sierra Leone. The union, on which the IMF has taken a dim view, had been scheduled to come on-stream in January 2003, but has been postponed till June 2005.