The United Nations Educational, Scientific and Cultural Organization (UNESCO) designates World Heritage Sites of outstanding universal value to cultural or natural heritage which have been nominated by countries which are signatories to the UNESCO World Heritage Convention, established in 1972. Cultural heritage consists of monuments, groups of buildings, and sites. Natural features, geological and physiographical formations, and natural sites which are important from the point of view of science, conservation or natural beauty, are defined as natural heritage. Greece ratified the convention on 17 July 1981, making its natural and cultural sites eligible for inclusion on the list.