The Secretary-General is appointed to a five-year term.
Although there is technically no limit to the number of five-year terms a Secretary-General may serve, the candidates, by convention serve two terms in office and are chosen on a rotational basis among the world’s geographic regions.
There is at present no concrete process, timeline or formal candidate criteria, although traditionally the Secretary-General has been selected based on an informal system of regional rotation, according to which the next Secretary General should come from Asia.
The UN Charter provides a rather uncomplicated selection process for the organisation's top post, which has since been supplemented by other procedural rules and accepted practices.
Article 97 of the Charter provides that the Secretary-General be appointed by the General Assembly upon a nomination from the Security Council.
The nominee must receive at least nine votes in the Council, including no veto from a permanent member.
This year, that includes permanent members China, France, Russia, the United Kingdom and the United States and rotating members Argentina, Congo, Denmark, Ghana, Greece, Japan, Peru, Qatar, Slovakia and Tanzania.
Rule 48 of the Provisional Rules of Procedure of the Security Council requires that the Council's deliberations on the nomination must be held in private session.
Similarly, Rule 141 of the Rules of Procedure of the General Assembly requires the Assembly's consideration of the Council's nominee to be discussed and voted on in closed session.
Advance discussion and political compromises behind closed doors generally ensure the nomination of a single candidate, usually from a middle power and with little prior fame.
While high profile candidates are frequently touted for the job, these are almost always rejected as unpalatable to some governments.
(Source: United Nations)