The Presidency of the Security Council is held in turn by the members of the Security Council in the English alphabetical order of their names. Each President holds office for one calendar month.
Ten non-permament members, elected by the General Assembly for two-year terms and not eligible for immediate re-election. The number of non-permanent members was increased from six to ten by an amendment of the Charter which came into force in 1965.
Each Council member has one vote. Decisions on procedural matters are made by an affirmative vote of at least nine of the 15 members. Decisions on substantive matters require nine votes, including the concurring votes of all five permanent members. This is the rule of "great Power unanimity", often referred to as the "veto" power.
Under the Charter, all Members of the United Nations agree to accept and carry out the decisions of the Security Council. While other organs of the United Nations make recommendations to Governments, the Council alone has the power to take decisions which Member States are obligated under the Charter to carry out.