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.
United Nations Security Council
The five permanent members of the Security Council were the victorious powers in World War II and have maintained the world's most powerful military forces ever since. They annually topped the list of countries with the highest military expenditures. In 2013, they spent over US$1 trillion combined on defence, accounting for over 55% of global military expenditures (the US alone accounting for over 35%). They are also among the world's largest arms exporters and are the only nations officially recognized as "nuclear-weapon states" under the Nuclear Non-Proliferation Treaty (NPT), though there are other states known or believed to be in possession of nuclear weapons.