An international organization, also known as an intergovernmental organization or an international institution, is an organization that is established by a treaty or other type of instrument governed by international law and possesses its own legal personality, such as the United Nations, the World Health Organization, International Union for Conservation of Nature, and NATO. International organizations are composed of primarily member states, but may also include other entities, such as other international organizations, firms, and nongovernmental organizations. Additionally, entities may hold observer status. An alternative definition is that an international organization is a stable set of norms and rules meant to govern the behavior of states and other actors in the international system.