Any UN member may join UNESCO. Other states may be admitted to UNESCO membership upon the recommendation of the organization's Executive Board and the approval of its General Conference by a two-thirds majority. Austria, Hungary, and Japan joined UNESCO years before entering the UN.
Under a United Kingdom-proposed amendment to the constitution adopted in 1951, territories or groups of territories not responsible for their international relations can be admitted as associate members upon application of member states or other authorities responsible for their international relations. Associate members do not have the right to vote.
A state may withdraw from UNESCO by notifying the organization's director-general of its intention to do so; the withdrawal takes effect as of the end of the respective calendar year. South Africa withdrew in December 1956 but rejoined in December 1994. Czechoslovakia, Hungary, and Poland suspended their participation in UNESCO activities in 1952 but returned as active participants in 1954. Portugal withdrew in 1972 but returned in 1974. In November 1974, a vote dominated by Arab and Communist delegations excluded Israel from UNESCO's European regional group and withheld aid from it on the ground that it persists "in altering the historic features" of Jerusalem during excavations—an allegation not sustained by UNESCO's archaeological expert.
At the end of 1984, the United States withdrew from UNESCO, stating that "trends in the policy, ideological emphasis, budget, and management of UNESCO were detracting from the organization's effectiveness." One year later, the United Kingdom and Singapore withdrew (the United Kingdom rejoined in 1997). In February 1994, the New York Times reported that the United States State Department had recommended that the US rejoin UNESCO, which had cut its staff by nearly 1,800 people and changed its stand on the controversial New World Information and Communications Order (NWICO). Until its departure, the United States had been responsible for 25% of UNESCO's budget. In September 2002, the United States announced it would rejoin UNESCO.
As of 2002, UNESCO had 188 members and 6 associate members.