Intergovernmental organization. Organizations that primarly consist of sovereign states, or other intergovernmental organizations. IGOs are created by a treaty or other agreement between two or more states that constitutes the charter of the group. Examples include the United Nations, the World Bank, the European Union, OPEC and FAO. IGOs participate as observers in UNFCCC negotiations (currently over 99 observers are IGOs).

www.intergovernmental organizations.org
Wikipedia.org (list of IGOs)
maindb.unfccc.int (list of admitted IGOs in UNFCCC negotiations)