The Joint Inspection Unit (JIU) is the only independent external oversight body of the United Nations system mandated to conduct evaluations, inspections and investigations system-wide.

Its mandate is to look at cross-cutting issues and to act as an agent for change across the United Nations system. JIU works to secure management and administrative efficiency and to promote greater coordination both between UN agencies and with other internal and external oversight bodies. For the past 50 years, the Unit has been dedicated to assisting the legislative bodies of numerous United Nations organizations in meeting their governance responsibilities. JIU provides support in the context of these agencies' oversight function regarding human, financial and other resources. In its reports and notes, the Unit identifies best practices, proposes benchmarks and facilitates information-sharing throughout the organizations of the UN system that have adopted its Statute.

The Unit operates with respect to the legislative organs and the secretariats of those specialized agencies and other international organizations, within the United Nations system, that have accepted its Statute. These entities are often referred to as the JIU participating organizations. JIU has a total of 28 participating organizations as of 2018 that play a crucial role in how the Unit functions.

Over the years, the Unit has contributed to several areas of work within the United Nations system with the objective to enhance management and administrative efficiency and to promote greater coordination among the United Nations organizations. Some of the key focus points have included executive management and other administrative matters (travel, procurement, common and shared services, etc.), human resource management, strategic planning and oversight.  Often JIU has developed benchmarks that helped the organizations to design or update their own management framework by reference to good practices in the system (results-based management, public information and communications, risk management, etc.). The JIU recommendations have also supported senior management teams of the UN organizations in their action to develop or review strategies and policies (knowledge management, public information and communications, information technology governance, multilingualism, etc.)