The Department of Peace Operations (DPO) (French: Département des opérations de maintien de la paix) is a department of the United Nations (UN) charged with the planning, preparation, management, and direction of UN peacekeeping operations. Previously known as the Department of Peacekeeping Operations (DPKO), it was created in 1992 as part of a restructuring of the UN's peace and security apparatus. The DPO retains the core functions and responsibilities of its predecessor, with a greater emphasis on cohesion, integrating different resources and knowledge, and promoting human rights.

With an annual budget of roughly $6.5 billion as of 2020, the DPO is the largest UN agency by expenditure, exceeding the UN's own regular budget. As of March 2020, it oversaw 81,370 personnel serving in 13 peacekeeping missions.

The DPO traces its roots to 1948 with the creation of the United Nations Military Observer Group for India and Pakistan (UNMOGIP) and the United Nations Truce Supervision Organization (UNTSO). Up to the late 1980s, peacekeeping missions were operated by six officials in the United Nations Office of Special Political Affairs, which was headed first by Under-Secretary-General Ralph Bunche, and subsequently Brian Urquhart and Marrack Goulding. From the beginning, peacekeeping operations operated with a clear doctrine that applied to its traditional or classical peacekeeping operations for inter-state ceasefires: peacekeepers did not take sides or discharge firearms, save in self-defense, or meddle in politics.

The Department of Peacekeeping Operations was created in March 1992 when Boutros Boutros-Ghali took office as Secretary-General of the United Nations; its creation was one of his first decisions. In organisational terms, it upgraded and expanded upon the work of the previous Field Administration and Logistics Division (FALD) (which remained active as a subordinate department). Goulding became under-secretary-general (or USG) for peacekeeping with Kofi Annan appointed as his deputy. The role of the DPKO, however, wasn't clarified until June 1992, when Boutrous-Ghali issued An Agenda for Peace, a plan to strengthen the UN's capacity for preventive diplomacy and peacekeeping.

French nationals have served as Under-Secretaries-General for Peacekeeping Operations since 1997.

At an October 2006 press conference, then USG Jean-Marie Guéhenno announced that peacekeeping operations had reached an all-time high, and would continue to expand as UNIFIL and UNMIT reached full strength, and if a UN mission were to enter Darfur.

As of 2010, DPO led 16 different missions in Africa, the Caribbean, the Middle East, Americas, Europe, and Asia. Serving in these missions were over 100,000 uniformed and civilian personnel. Total approved annual expenses were over US$5 billion for the period July 2006 to June 2007.

DPO is split into two main offices: the Office of Operations and the Office of Mission Support (OMS).