The United Nations Mission in Liberia (UNMIL) was a United Nations peacekeeping operation established in September 2003 to monitor a ceasefire agreement in Liberia following the resignation of President Charles Taylor and the conclusion of the Second Liberian Civil War (1999–2003). At its peak it consisted of up to 15,000 UN military personnel and 1,115 police officers, along with civilian political advisors and aid workers.

Peacekeeping by the United Nations is a role of the UN's Department of Peace Operations as an "instrument developed by the organization as a way to help countries torn by conflict to create the conditions for lasting peace". It is distinguished from peacebuilding, peacemaking, and peace enforcement although the United Nations does acknowledge that all activities are "mutually reinforcing" and that overlap between them is frequent in practice.