To expedite decision and action, the membership of the Security Council was deliberately restricted to a small number. Originally an 11-member body, it was subsequently enlarged to 15 members by a charter amendment that came into effect on 31 August 1965.
With five seats permanently assigned, the remaining 10 are filled by other UN members elected by secret ballot in the General Assembly for two-year terms. Five seats on the Security Council become vacant each year. Nonpermanent members of the council are ineligible for immediate reelection upon retirement. In electing the nonpermanent members of the Security Council, the General Assembly is required to pay due regard to the past and potential contribution of nations to the maintenance of international peace and security, as well as to equitable geographical distribution. In view of the power of the council, nations attach great importance to the choice of the nonpermanent members.
The problem of ensuring equitable geographical distribution of members elected to the Security Council has not been easy to resolve. Prior to the council's enlargement, there had been a longstanding difference of views on a "gentlemen's agreement" reached in the early days of the UN that was intended to guarantee that the six nonpermanent seats would be so distributed that one of the seats would always be held by a Soviet bloc country. However, until 1960, only Poland and the Ukraine were elected, and each served for only one two-year term. In the 1959 election, Poland and Turkey competed for the nonpermanent council seat for the two-year term 1960–61. After 52 ballots, the General Assembly gave the seat to Poland on the basis of the following compromise: though elected for two years, Poland would resign its seat at the end of the first year and Turkey would be the sole candidate to fill the unexpired term. Under a similar arrangement, Romania held a seat for 1962, resigning it for 1963 to the Philippines. To avoid the recurrence of such situations after the enlargement of the council, the General Assembly established a fixed pattern for the geographical distribution of the 10 nonpermanent seats: five from African and Asian nations, one from East European nations, two from Latin American and Caribbean nations, and two from West European and other nations.
The accession of the Russian Federation, a vastly less powerful state than the former USSR, to a permanent seat on the Security Council set off a discussion among the UN membership about the need to make changes to the structure of the Security Council to better reflect the radical changes in the world and the organization's overall membership. The 48th General Assembly established an Open-Ended Working Group on the Question of Equitable Representation on and Increase in the Membership of the Security Council, which held its first meeting in New York on 19 January 1994. The Working Group submitted an informal report to the Secretary-General summarizing the results of its survey of the membership. It found that virtually all member states of the UN favored an increase in the membership of the Security Council. There was little unanimity, however, on the criteria for revising the council's composition. Responses received by the Working Group proposed increasing membership by as few as four (to 19) or more than doubling its size (to 31). Some members suggested the number of permanent members be increased at least by one (to six), or perhaps as much as seven (to 12). Most states responding to the survey agreed that an increase in membership should not diminish the council's efficiency. While most members favored continuing the categories of permanent and nonpermanent memberships, new categories were suggested: permanent seats without power of veto; rotating permanent seats, with or without power of veto; and semipermanent seats or extended membership. Some of the possible criteria put forward for new Security Council permanent membership included size of peacekeeping and financial contributions, the size of population and territory, economic potential, regional importance, geopolitical situation, and military capability.
In 2002, the Security Council consisted of the five permanent members: China, France, the Russian Federation, the United Kingdom, and the United States; the 10 nonpermanent members, elected for a two-year period, were Bulgaria, Cameroon, Colombia, Guinea, Ireland, Mauritius, Mexico, Norway, Singapore, and the Syrian Arab Republic.