- Member states of the United Nations
- Membership in the United Nations is open to all other peace-loving states which accept the obligations contained in the present Charter and, in the judgment of the Organization, are able and willing to carry out these obligations.
- The admission of any such state to membership in the United Nations will be effected by a decision of the General Assembly upon the recommendation of the Security Council.
A recommendation for admission from the Security Council requires affirmative votes from at least nine of the council's fifteen members, with none of the five permanent members voting against. The Security Council's recommendation must then be subsequently approved in the General Assembly by a two-thirds majority vote.
In principle, only sovereign states can become UN members, and currently all UN members are sovereign states (although a few members were not sovereign when they joined the UN). Vatican City is the only sovereign state with general international recognition that is not a UN member (the Holy See, which holds sovereignty over the state of Vatican City and maintains diplomatic relations with other states, is a UN permanent observer). Because a state can only be admitted to the UN by the approval of the Security Council and the General Assembly, a number of states that may be considered sovereign states according to the Montevideo Convention criteria are not members because the UN does not consider them to possess sovereignty, mainly due to the lack of international recognition or opposition from certain members.
In addition to the member states, the UN also invites non-member states, intergovernmental organizations, and other international organizations and entities whose statehood or sovereignty are not precisely defined, to become observers at the General Assembly, allowing them to participate and speak, but not vote, in General Assembly meetings.
The UN officially came into existence on 24 October 1945, after ratification of the United Nations Charter by the five permanent members of the United Nations Security Council (the Republic of China, France, the Soviet Union, the United Kingdom, and the United States) and a majority of the other signatories. A total of 51 original members (or founding members) joined that year; 50 of them signed the Charter at the United Nations Conference on International Organization in San Francisco on 26 June 1945, while Poland, which was not represented at the conference, signed it on 15 October 1945.
Among the original members, 49 are either still UN members or had their memberships in the UN continued by a successor state (see table below); for example, the membership of the Soviet Union was continued by the Russian Federation after its dissolution (see the section Former members: Union of Soviet Socialist Republics). The other two original members, Czechoslovakia and Yugoslavia (i.e., the Socialist Federal Republic of Yugoslavia), had been dissolved and their memberships in the UN not continued by any successor state (see the sections Former members: Czechoslovakia and Former members: Yugoslavia).
At the time of UN's founding, the seat of China in the UN was held by the Republic of China, but as a result of United Nations General Assembly Resolution 2758, it is now held by the People's Republic of China (see the section Former members: Republic of China).
A number of the original members were not sovereign when they joined the UN, and only gained full independence later:
- Belarus (then the Byelorussian Soviet Socialist Republic) and Ukraine (then the Ukrainian Soviet Socialist Republic) were both constituent republics of the Soviet Union, until gaining full independence in 1991.
- India (whose territory at that time, before the partition of India, also included the present-day territories of Pakistan and Bangladesh) was under British colonial rule, until gaining full independence in 1947.
- The Philippines (then the Philippine Commonwealth) was a commonwealth with the United States, until gaining full independence in 1946.
- New Zealan