The United Nations Office of Internal Oversight Services (OIOS) is an independent office in the United Nations Secretariat whose mandate is to "assist the Secretary-General in fulfilling his internal oversight responsibilities in respect of the resources and staff of the Organization.

"[1] Specifically, activities include internal audit, investigation, monitoring, evaluation, inspection, reporting and support services to the United Nations Secretariat.

[4] The office was established in 1994 at the insistence of the United States that the UN take steps to curb waste and corruption, although there are some doubts concerning its effectiveness.

OIOS adds value by providing world-wide audit, investigation, inspection, programme monitoring, evaluation and consulting services to the United Nations Secretariat and a wide range of United Nations operational funds, programmes and tribunals.

OIOS sees itself as an agent of change, committed to help client departments and offices bring about responsible administration of resources and a culture of accountability, transparency, results-orientation and risk awareness.