This article focuses on the United Nations Observer Group in Central America (ONUCA), a peacekeeping mission deployed by the UN Security Council from November 1989 to January 1992 to monitor the implementation of a far-reaching peace agreement (known as the “Esquipulas II Agreement”) following almost three decades of civil war, violence, and authoritarianism in Guatemala, Honduras, Costa Rica, El Salvador, and Nicaragua. After providing an overview of the conflicts in the five Central American countries, the article outlines ONUCA’s mandate as well as its operational achievements and limitations in terms of confidence-building, ceasefire monitoring, separation of forces, disarmament, and demobilization. It also discusses the lessons that can be learned from ONUCA’s experience.