The Organisation of Eastern Caribbean States (OECS; French: Organisation des États de la Caraïbe orientale, OECO) is an inter-governmental organisation dedicated to economic harmonisation and integration, protection of human and legal rights, and the encouragement of good governance between countries and territories in the Eastern Caribbean. It also performs the role of spreading responsibility and liability in the event of natural disaster.
The Organisation was established by the Treaty of Basseterre on 18 June 1981. The administrative body of the OECS is the Commission, which is based in Castries, the capital of Saint Lucia.
OECS currently has eleven members which together form a continuous archipelago across the Leeward Islands and Windward Islands. Anguilla, the British Virgin Islands, Guadeloupe and Martinique are only associate members of OECS. Diplomatic missions of the OECS do not represent the associate members. For all other purposes, associate members are treated as equals of full members.
Six of the members were formerly colonies of the United Kingdom. Three others, Anguilla, the British Virgin Islands, and Montserrat remain overseas territories of the UK while Martinique and Guadeloupe are French departments and regions of France. Eight of the eleven members are constitutional monarchies with Queen Elizabeth II as their current monarch (Dominica is a republic with a President). There is no requirement for the members to have been British colonies; however, the close historical, cultural and economic relationship fostered by almost all of them having been British colonies is as much a factor in the membership of the OECS as their geographical proximity.