It is undisputed that international organizations can take decisions that are binding upon their Member States and that they can even exercise sovereign powers.1 This is evident in such organizations as, for example, the United Nations (UN), the European Union (EU), the World Health Organization (WHO), the International Civil Aviation Organization (ICAO), the Organization of American States (OAS), the North-Atlantic Treaty Organization (NATO), the Organisation for Economic Co-operation and Development (OECD), the Universal Postal Union (UPU), the World Meteorological Organization (WMO), and the International Monetary Fund (IMF).  Traditionally, analyses of the law-making powers of international organizations started from three propositions: (1) member states provide the international organizations they establish with the law-making powers as they see fit, laid down in the constituent instrument of the organization (constituent treaty); (2) international organizations have only the law-making powers that have been attributed to them in the constituent treaty by their member states (doctrine of attributed powers); and (3) the law-making powers of international organizations are generally limited to internal matters. Recent developments suggest, however, that these traditional propositions no longer hold true.
This applies in the first place to the constituent instruments establishing international organizations. Like all national and international norms, they are subject to interpretation by the parties and organs applying it. It is possible, therefore, that these constituent instruments, including their provisions pertaining to the law-making powers of the organization, will be construed in a different way than was originally intended by the drafting nations, as it proves very difficult to draft an instrument in such a manner as to effectively preclude any other possible interpretation. As Boisson de Chazournes and Gadkowsky observe in their annotation of the International Court of Justice’s (ICJ) 1986 judgment in Military and Paramilitary Activities in and against Nicaragua, resolutions of international organizations constitute an important tool for such treaty interpretation.
Secondly, (certain) acts of international organizations are increasingly having normative repercussions beyond their concrete scope of application. A good example is the manner in which UN General Assembly resolutions are seen as evidence of customary international law by the ICJ in Military and Paramilitary Activities in and against Nicaragua (Boisson de Chazournes and Gadkowski) and in other cases.
Thirdly, the stronger frequency, intensity, and impact of law-making by international organizations has given rise to unprecedented dynamics before international, supranational, and national courts. The least one can say in this respect is that supremacy clauses do not, or not any longer, inspire enough awe in order for international and national courts to stay passive in the face of international institutional action when constitutional values are at stake. In particular, courts may refrain from giving effect to art. 103 of the UN Charter, which provides that ‘[i]n the event of a conflict between the obligations of the Members of the United Nations under the present Charter and their obligations under any other international agreement, their obligations under the present Charter shall prevail’, where rival obligations pertain to the protection of fundamental rights. At the international level, one of the first cases in a UN context in this respect was the ICJ’s 1971 Advisory Opinion on the Legal Consequences for States of the Continued Presence of South Africa in Namibia. The opinion touches upon the role of the ICJ in exercising a review over the factual and legal determinations of other principal UN organs, including the General Assembly and the Security Council (McGonigle Leyh).
Especially before European domestic and EU courts, a more intense awareness of the implications of acts of international organizations for the legal position of individuals and for deeply-held constitutional values of domestic legal orders has given rise to interesting judicial dynamics since the mid-1970s. Various strings of cases have generated true ‘sagas’ in which a critical constitutional dialectic between norms of international organizations and a domestic legal order unfolded before the courts. The most classical example of such a saga in the relationship between EU law and national law has been, since the 1970s, the Solange case-law of the German Constitutional Court, the Bundesverfassungsgericht (Hilpold). But over the past ten years, an even more fascinating saga sent shockwaves through the relationship between the legal orders of two important international organizations: the UN and the EU. These were the Kadi cases (Tzanakopoulos), in which—in a manner not dissimilar to the attitude of the German Constitutional Court vis-a-vis EU law—the ECJ refused to relinquish its control power over EU acts implementing UN Security Council decisions on terrorist blacklisting as long as the UN cannot assure comparable fundamental rights guarantees. Last but not least, the Security Council’s terrorist blacklisting practice also gave rise to a clash with the Swiss Federal Tribunal in its 2007 decision in Nada, one of the first cases to challenge Security Council sanctions under Chapter VII before a national court, and which found an extension in the European Court of Human Rights 2012 Grand Chamber judgment in this case (Hilpold).
-  Part of the analysis in this introduction relies on J. Wouters and Ph. De Man, ‘InternationalOrganizations as Law-Makers’, in J. Klabbers and A. Wallendahl (eds), Research Handbook onInternational Organizations Law: Between Functionalism and Constitutionalism (Cheltenham, EdwardElgar Publishing 2011), pp. 190-224.
-  R.A. Wessel and J. Wouters, ‘The Phenomenon of Multilevel Regulation: Interactions BetweenGlobal, EU and National Regulatory Spheres’ in A. Follesdal, R.A. Wessel, and J. Wouters (eds),Multilevel Regulation and the EU. The Interplay Between Global, European and National NormativeProcesses (Leiden, MNP 2008), p. 13. See further, D. Sarooshi, International Organizations and theirExercise of Sovereign Powers (Oxford, Oxford University Press 2005) and C.F. Amerasinghe, Principlesof the Institutional Law of International Organizations (Cambridge, Cambridge University Press 2005).
-  J.E. Alvarez, International Organizations as Law-makers (Oxford, Oxford University Press 2006), pp. 120-1.
-  See also Introduction to Part 2—Legal Powers—of this volume.
-  See, more generally, D.C. Smith, ‘Beyond Indeterminacy and Self-contradiction in Law: TransnationalAbductions and Treaty Interpretation in U.S. v. AlvareZ-Machain, (1995) 6 European Journal ofInternational Law 1.