The United Nations Security Council normally creates and defines peacekeeping missions. It does this by providing the mission with a mandate—a description of the mission's tasks. To establish a new peacekeeping mission, or change the mandate or strength of an existing mission, nine of the Security Council's 15 Member States must vote in favour.

However, if any one of the five permanent members—China, France, the Russian Federation, the United Kingdom or the United States—votes against the proposal, it fails.

The Department of Peacekeeping Operations directs and manages the missions on behalf of the Secretary-General, who reports to the Council on their progress. Most missions are headed by a Special Representative of the Secretary-General. DPKO assists the Secretary-General in formulating policies and procedures for peacekeeping, making recommendations on the establishment of new missions and in managing ongoing missions. The Department also supports a number of political missions, such as the UN Assistance Mission in Afghanistan, the UN Office in Timor-Leste and the UN Integrated Office in Sierra Leone.

Senior military officers, staff officers and military observers serving on United Nations missions are directly employed by the UN—usually on secondment from their national armed forces. Peacekeeping troops, popularly known as Blue Helmets, participate in UN peacekeeping under terms that are carefully negotiated by their Governments and remain under the overall authority of those Governments while serving under UN operational command.

The authority to deploy peacekeepers remains with the Government that volunteered them, as does responsibility for pay, disciplinary and personnel matters.

Police officers are also contributed by Member States and serve on the same basis as military observers, that is as “experts on mission” paid by the United Nations.

The Security Council may also give its authorization to peacekeeping operations that are carried out by other bodies. In 1999, for example, once the NATO bombing campaign was over, the Council authorized NATO to keep the peace in Kosovo (as the Kosovo Force or KFOR). At the same time, the Council set up the United Nations Interim Administration Mission in Kosovo (UNMIK)—a UN peacekeeping operation—and tasked it with administering the territory, ensuring law and order and creating democratic institutions of self-government. The same year, the Council authorized an international force led by Australia to restore security in East Timor, now Timor-Leste. That force was replaced the following year by a UN peacekeeping operation. In 2001, the Council authorized an international coalition—the International Security Assistance Force (ISAF)—to maintain a military presence in Afghanistan, while also setting up a UN political mission to support the transitional government. In October 2003, the Council authorized a US-led multinational force to maintain security and stability in Iraq. The Council in 2004 asked the African Union to monitor the situation in Darfur, Sudan, while peace was sought through talks between the parties.