There are 193 United Nations (UN) member states, and each of them is a member of the United Nations General Assembly.

The criteria for admission of new members are set out in the United Nations Charter, Chapter II, Article 4, as follows:

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.