The term common system is shorthand for the United Nations common system of salaries, allowances and other conditions of service. Its origin can be traced to the relationship agreements concluded between the United Nations and the specialized agencies. While the wording of these agreements varies, most of them carry language to the effect that it is agreed to develop common personnel standards, methods and arrangements designed to avoid serious discrepancies in terms and conditions of employment, to avoid competition in recruitment of personnel and to facilitate the interchange of personnel.
The common system was intended to prevent competition among the organizations in staff recruitment and to facilitate exchange of staff. Other rationales for a common system include:
Efficiency/economy of scale: central maintenance of salary scales and allowance schedules means far fewer resources have to be deployed for these purposes in each organization;
Equity/fairness: morale can be jeopardized when staff working side by side have different conditions of service -- a uniform approach lessens such dissatisfaction;
Cost-efficiency/control: for the Member States, a common set of employment conditions permits an overview of staff costs.
The system comprises the United Nations, its affiliated programmes, thirteen specialized agencies, and one organization with a special status under the ICSC statute. The World Bank Group and the International Monetary Fund (also known as the Bretton Woods institutions) are not part of the common system.
Staff statistics of United Nations Common System Organizations (Tables) can be found in the Chief Executives Board for Coordination (CEB) website: CEB Annual reports
| ORGANIZATION | HEADQUARTERS | |
 | United Nations (UN) | New York |
 | United Nations Development Programme (UNDP)* | New York |
 | United Nations Population Fund (UNFPA)* | New York |
 | United Nations Office for Project Services (UNOPS)* | Copenhagen |
 | United Nations High Commissioner for Refugees (UNHCR)* | Geneva |
 | United Nations Children's Fund (UNICEF)* | New York |
 | United Nations Relief and Works Agency for Palestine Refugees in the Near East (UNRWA) * | Gaza |
 | International Trade Centre (ITC)* | Geneva |
 | International Labour Organization (ILO) | Geneva |
 | Food and Agriculture Organization (FAO) | Rome |
 | World Food Programme (WFP)* | Rome |
 | United Nations Educational, Scientific and Cultural Organization (UNESCO) | Paris |
 | World Health Organization (WHO) | Geneva |
 | International Civil Aviation Organization (ICAO) | Montreal |
 | Universal Postal Union (UPU) | Bern |
 | International Telecommunication Union (ITU) | Geneva |
 | World Meteorological Organization (WMO) | Geneva |
 | International Maritime Organization (IMO) | London |
 | World Intellectual Property Organization (WIPO) | Geneva |
 | International Fund for Agricultural Development (IFAD) | Rome |
 | United Nations Industrial Development Organization (UNIDO) | Vienna |
 | International Atomic Energy Agency (IAEA) | Vienna |
 | World Tourism Organization (UNWTO) | Madrid |
 | UN Women (UNWomen)* | New York |
 | International Seabed Authority (ISA) | Jamaica |
 | United Nations Programme on HIV/AIDS (UNAIDS) * | Geneva |
 | International Tribunal for the Law of the Sea | Germany |
* Affiliated programmes of the UN.
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