The Security Council is a permanent body of the United Nations tasked to maintain international peace and security. It has the power to enforce measures and functions continuously at the seat of the UN. The council consists of fifteen members, of which five: China, France, Russia, the UK, and the U.S., are permanent and have the power of veto. The other 10 (originally six) non-permanent members are elected for two-year terms by the General Assembly; equitable geographic distribution is required. Customarily there are five non-permanent members from African and Asian states, one from Eastern Europe, two from Latin America, and two from Western Europe and elsewhere. In the council the presidency is occupied for one-month terms in the alphabetical order of the members' names in English.

The UN commission proposed changes to the council in 1997, including adding five new permanent members without veto powers, adding four additional non-permanent members, and placing restrictions on the use of the veto. The proposed changes were regarded by many nations as a groundwork for negotiations on the eventual restructuring of the council. Brazil, Germany, India, Japan, and South Africa have sought permanent seats on the council, and in July, 2005, the first four nations submitted a General Assembly resolution calling for the expansion of the council, but not for veto-power for new permanent members. The African Union, however, has called for new permanent members to have the veto and for Africa to receive two permanent seats. There has been no significant progress on the issue, but in Sept., 2008, the General Assembly unanimously called for intergovernmental negotiations on the enlargement of the council, which began in Feb., 2009.

There are two voting systems in the Security Council. On procedural matters the affirmative vote of any nine members is necessary, but on substantive matters the nine affirmative votes required must include those of the five permanent members. This requirement of Big Five unanimity embodies the so-called veto. In practice the council has, on most substantive matters, not treated an abstention by a permanent member as a veto. In two situations, however, those of recommending applicants for UN membership and of approving proposed amendments to the charter, the actual concurrence of all permanent members has been required. The veto has prevented much substantive action by the UN, but it embodies the reality that resolution of major crises requires agreement of the major powers.

The Security Council may take measures on any danger to world peace. It may act upon complaint of a member or of a nonmember, on notification by the secretary-general or by the General Assembly, or of its own volition. In general the council considers matters of two levels of significance. For disputes or situations that may give rise to them that might endanger peace, the council is limited to making recommendations to the parties after it has exhausted other methods of reaching a solution. In the case of more serious matters, such as "threats to the peace," "breaches of the peace," and "acts of aggression," the council may take enforcement measures. These may range from full or partial rupture of economic or diplomatic relations to military operations of any scope deemed necessary. By the terms of the charter, the UN was forbidden to intervene in matters which are essentially domestic, but this limitation was not intended to hinder Security Council measures to prevent threats to peace. The charter was intentionally ambiguous regarding domestic issues that could also be construed as threats to peace and left a potential opening for intervention in domestic issues that threaten to have dangerous international repercussions.