United Nations System
There are 15 members of the Security Council, consisting of five veto-wielding permanent members (China, France, Russia, the United Kingdom, and the United States) and 10 elected non-permanent members with two-year terms. This basic structure is set out in Chapter V of the UN Charter. Security Council members must always be present at UN headquarters in New York so that the Security Council can meet at any time.
Charter of the United Nations
2. The non-permanent members of the Security Council shall be elected for a term of two years. In the first election of the non-permanent members after the increase of the membership of the Security Council from eleven to fifteen, two of the four additional members shall be chosen for a term of one year. A retiring member shall not be eligible for immediate re-election.