The United Nations Office of Internal Oversight Services (OIOS) is the internal oversight body of the United Nations. Established in 1994 by the General Assembly, the Office assists the Secretary-General in fulfilling his oversight responsibilities in respect of the resources and staff of the Organization through the provision of audit, investigation, inspection and evaluation services.

To carry-out its work, the Office is organized into the following functional units:

1. Internal Audit Division - audit assesses the adequacy and effectiveness of internal controls for the purpose of improving the Organization’s risk management, control and governance processes.
2. Inspection and Evaluation Division - evaluation assesses the relevance, efficiency and effectiveness (including impact) of the Organization’s programmes in relation to their objectives and mandates. 
3. Investigations Division - investigation establishes facts related to reports of possible misconduct to guide the Secretary-General on jurisdictional or disciplinary action to be taken.
4. Leadership - the Office is headed by the Under-Secretary-General for Internal Oversight Services, Ms. Heidi Mendoza, who is appointed by the Secretary-General, following consultations with Member States, and approved by the General Assembly for one five-year term without possibility of renewal. 
5. Coordination and Cooperation - OIOS covers all United Nations activities under the Secretary-General's authority, including: the UN Secretariat in New York, Geneva, Nairobi and Vienna, five regional commissions, peacekeeping missions and humanitarian operations; assistance to Funds and Programmes administered separately under the authority of the Secretary-General (including UNHCR, UNEP, UN HABITAT, and OHCHR), and other entities that have requested OIOS services such as UNCCD and UNFCCC.