An international organization or international organisation (see spelling differences), also known as an intergovernmental organization or an international institution, is a stable set of norms and rules meant to govern the behavior of states and other actors in the international system. Organizations may be established by a treaty or be an instrument governed by international law and possessing its own legal personality, such as the United Nations, the World Health Organization 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 (including states) may hold observer status.