Normally, the Security Council authorizes a peacekeeping operation for a set initial time period of six months to a year. The Council meets periodically to review implementation of the mandate and to discuss the changing situation on the ground, as presented and analyzed by the Secretary-General in his regular reports. Based on the Secretary-General's recommendations, and the views of Council members, the Security Council will vote to extend, expand, reduce, change or withdraw a peacekeeping operation. When a mandate is deemed completed and after consultations with the parties involved, the Council will vote to end the mission, as most recently in Sierra Leone and Timor-Leste.

Most of the missions established in the last 15 years have been set up to implement already signed peace agreements with a clearly identified UN role, timeframe and benchmarks for their implementation, thus making the stay of the UN operation on the ground predictable and finite.

During the Cold War, however, when it was more common for peacekeeping operations to be interposed between two former warring states pending the negotiation of a peace agreement, the presence of peacekeepers sometimes had the unintended effect of reducing pressure on the parties to make the necessary compromises. The results, in some cases, were that the status quo continued for decades and the peacekeepers were left in place much longer than originally envisaged.

On the other hand, in the early 1990s, missions tended to be ended as soon as a landmark election was completed or new government installed. Current thinking is that establishing sustainable peace takes longer and that other benchmarks should be required before peacekeepers withdraw completely.

In each particular case of a long-standing mission, the Security Council has to carefully weigh the alternatives to the continuing presence of a UN peacekeeping mission in the absence of a firm peace and/or security. In most cases, the possibility of the resumption of conflict or destabilization of a country or region may be judged unacceptably high.

Out of the 13 operations established by the United Nations from 1948 to 1988, five are still deployed. They are mostly in the Middle East, where peacekeepers continue to monitor boundaries in a region prone to tensions; but also in the State of Jammu and Kashmir where the UN supervises the ceasefire between India and Pakistan; and in Cyprus where the Turkish and Greek Cypriots have yet to resolve their dispute over the island.