Intergovernmental organizations (IGOs) are permanent associations of states created by states on the basis of a treaty or constituent instrument (charter, constitution, statute, or covenant) for the performance of certain goals of common interest as defined in that instrument and governed by public international law.
IGOs have legal personalities separate from their member states, i.e., corporate or governmental entities. The international legal status of IGOs enables them to enter into agreements with other IGOs or states. IGOs may have a general mission (i.e., U.N.), a specific purpose (i.e., WTO), or a regional focus (i.e., OAS, ECOWAS).
Another critical function of an IGO is as a forum for the adoption of multilateral conventions. In the past, states convened international conferences to address specific international problems. While that practice still exists, international relations have become “institutionalized.” There are now existing, permanent IGOs that specialize in certain areas. Those IGOs naturally serve as forums for the adoption of new conventions in those areas. IGOs may serve as depositories for treaties and help draft new treaties on specific topics, thereby promoting the development of international law. IGO websites are often quite useful for treaty research.
Note that the documentation of IGOs (like, i.e., the U.N.) is not listed as a source of law under Article 38 of the Statute of the International Court of Justice but has become increasingly important to the development of international law. IGO documentation has sometimes been termed “soft law” as it is not binding in the same sense as true legislation. It may, however, be indicative of custom, for example.
Over the years, the actions, decisions, and resolutions of IGOs have become an additional “fifth” source of international law. International organizations play a crucial role in establishing and enforcing international law. They establish and promote conventions between nations; some adjudicate cases and issue decisions by which nations agree to be bound.
Like federal agencies, IGOs have legislative, executive (or administrative), and judicial functions. In the context of international law, the term “legislative” must be used cautiously, because few IGOs are empowered to take binding action. Rather, most organizations can only make recommendations, which are nonbinding acts. This capacity to adopt norms, whether binding or not, is considered a basic element of an IGO.
Many normative acts of IGOs concern the internal functioning of the organization itself. However, some acts may bind members in the external sphere. For example, UN Security Council resolutions may be considered “decisions” within Article 25 of the UN Charter and, therefore, binding on member states.
Non-governmental Organizations (NGOs) are private, nonprofit organizations established by individuals and national associations to coordinate their cooperation on an international level in a given field of activity. NGOs are independent of any particular government. i.e., Greenpeace and Amnesty International. Since they are not endowed with governmental powers, NGOs cannot enter into treaties or international agreements in contrast with IGOs.
A supranational organization may enact rules that preempt laws of the member states and may grant rights to nationals of member states which such nationals may directly invoke. The European Union is the world's only true supranational organization.