‘Legal powers’ make it possible for international organizations to act and in so doing to become ‘living’ entities in the legal world as well as in social reality. A ‘legal power’ is neither more nor less than the ability to perform all kind of acts, that is buying or renting a building to accommodate the organization or the adoption by an organ of an organization of sanctions against a state. In international documents and literature legal powers are also termed ‘capacities’, ‘competences’, or even ‘rights’. From a legal point of view the most important powers are those that confer on organs of an international organization the power to perform legal acts, that is the capacity to take decisions with a certain normative force; for instance the establishment by an international organization of a judicial organ for the settlement of disputes with its administrative staff, the approval of the budget by an organ of an international organization, the call of an international organization to its members to refrain from the use of nuclear weapons, the promise of an international organization to send doctors, nurses, and medical equipment to a disaster area, etc.
Of course, only international organizations with the status of an international legal person, as discussed in the First Part, can have legal powers. Holding otherwise would be problematic, because an international organization without international legal personality does not exist as a separate entity in the international legal system and cannot, as such, have or perform legal powers. At the same time, having certain legal powers is sometimes also seen as a strong indication that the international organization concerned does exist as an international legal person. As discussed, the International Court of Justice observed in its advisory opinion in the Reparation for Injuries case that the United Nations was entrusted with a whole range of specific legal powers, which could practically only be carried out if the organization did possess international legal personality.1
Legal powers define to a large extent the character and functioning of an international organization. There are (a lot of) international organizations with no other purpose than to co-ordinate the actions of their member states in certain policy areas and to that end dispose merely of hortatory powers, powers to induce or recommend their member states to carry out certain courses of action. Although such powers are regularly cast in rather vague terms and the scope or limitation of such powers is not always clear, the performance of such powers will usually not lead to disputes before (international) courts or tribunals. That is different with regard to international organizations with aims that go beyond the mere co-operation between the member 
states, such as the United Nations, some of its specialized agencies like the World Health Organization, and several regional organizations, with the European Union as the most outspoken one.
These ‘supra-national’ or ‘integration’ organizations have far-reaching legal powers in their fields of competence, related to, for instance, the elaboration or the creation of international rules, the implementation and maintenance of such rules, and/ or the judicial or quasi-j udicial settlement of disputes. The use of these powers can really affect, directly or indirectly, the position of the member states or of other actors, including citizens and private entities. And thus it is not surprising that, at least in some situations, the (intended) exercise of these powers, through for instance the (proposed) adoption of a decision by an organ of an organization, results in discussions, and even serious conflicts. Such conflicts can occur between member states inter se, between member states and the organ, or between organs of the organization and can be related to various ‘constitutional’ issues, such as the legal foundation(s) of the powers of the organization, the division of powers between organs of the organization, and, last but not least, the scope and limitations of the powers.
One can say, the stronger the powers of international organizations, the stronger the fear for improper use or misuse of those powers. To some extent the legal regime of powers itself can provide for certain guarantees in that respect, above all by formulating the power-conferring rules as precise as possible. However, other fields of international institutional law will be of utmost importance for the protection against improper use or misuse of powers, such as the regimes concerning decision-making, responsibility, and judicial remedies.
The controversies about the foundation and scope of the powers of international organizations are to some extent related to the differences in the approach of the legal character of international organizations. According to the traditional school of thought—approaching international organizations primarily as state driven entities—the powers of international organizations are, explicitly or implicitly, attributed to them by the member states via the founding treaty and other constitutive instruments. Such an approach tends to favour a restrictive interpretation of the legal powers. The other school of thought views international organizations primarily as autonomous legal persons and maintains that their powers are inherently vested in the organizations themselves; they comprise all those powers—explicitly or implicitly stated—that are necessary to realize the objectives and functions of the organization. Because of the fundamental dual character of international organizations, namely as an alliance of states and as a relatively independent legal person, it seems self-evident to see the two aforementioned views on the foundations of the powers of international organizations as complementary rather than as mutually exclusive.
Be that as it may, the judgments and opinions of international courts on the legal powers of international organizations—including the four cases commented upon in this Part—can best be understood as attempts to find an adequate balance between the two approaches. That holds also true for the advisory opinion in the Reparation for Injuries case, which is extensively discussed in the former Part of this volume but is at least as important for the foundation and scope of the legal powers of international organizations. In its opinion from 1949, the International Court of Justice made the following—now famous—observation:
Under international law, the Organisation must be deemed to have those powers
which, though not expressly provided in the Charter, are conferred upon it by necessary implication as being essential to the performance of its duties.
The recognition by the Court of the principle or doctrine of implied powers has been by far its most important decision for the development of the legal powers of, first, the United Nations and, gradually, nearly all international organizations. Also where the principle of attribution is expressly stated in the basic treaty as the legal foundation of its powers, such as in the Treaty on European Union, claims of implied powers arise and are awarded. Not every situation is foreseeable and thus organizations—including their member states—are confronted with gaps in the legal power regime and with the question whether the powers of the organization should be extended without formally amending the basic treaty. Consequently, the doctrine of implied powers, in particular its foundation and scope, is among the most discussed issues of international institutional law, and also in legal practice. All the cases discussed in this Part are linked to the doctrine of implied powers, as holds true for some cases in other Parts of this volume.
The doctrine of implied powers was not new in 1949. It was applied in some national legal systems and, more significantly, by the Permanent Court of International Justice in relation to a specific international organization, a Mixed Commission of Greece and Turkey for the settlement of some (territorial) issues. That as such was quite remarkable, given the strict positivistic legal approach of the Permanent Court towards international law. Only one year earlier the Permanent Court very clearly expressed its approach in the following sentence in its judgment in the SS Lotus case: ‘Restrictions upon the independence of States cannot [...] be presumed.’ Therefore it is worthwhile to see how the Permanent Court formulated and applied the notion of implied powers in its opinion concerning the Interpretation of the Greco-Turkish Agreement of 1 December 1926 (Montejo), the first case discussed in this Part. It is suggested that the Permanent Court in effect did nothing more than make an interpretation of an existent power provision in the agreement concerned, and thus, if it applied implied powers at all, it applied the doctrine in—what later is called—a restricted way by deducing the implied power from an expressly attributed power.
Already in the Reparation for Injuries case, the International Court of Justice made use of a wider and more flexible version of the implied powers doctrine by accepting the existence of a tacit power on the basis of a functional analysis of the objectives and tasks of the organization. Later, it had the chance to develop its liberal approach in a number of cases, of which three are commented upon in this section. In the first two opinions—Effect of Awards of Compensation Made by the United Nations Administrative Tribunal (Keith) and Certain Expenses of the United Nations (Article 17, Paragraph 2, of the Charter) (Wouters and Odermatt)—the Court accepted, inter alia, claims of competences of the General Assembly to establish an administrative tribunal and a peace-keeping force, notwithstanding the silence of the Charter as to those claims. The most controversial opinion in this regard certainly is given by the Court on request of the Assembly of the World Health Organization in the case of the Legality of the Use by a State of Nuclear Weapons in Armed Conflict (WHO Opinion, Burci and Quirin). It is the first and until now sole case in which the Court, without abandoning its implied powers doctrine, clearly addressed—and enforced—restrictions to the extension of powers of international organizations.
The cases in this Part are not only chosen for their relevance to the implied powers doctrine but also because of their significance for some other aspects of the legal powers of international organizations: the delegation of powers is addressed in the Effect of Awards case; the division of legal powers between organs of an international organization is a central element in the Certain Expenses case; the division of legal powers between the United Nations and one of its specialized agencies, the World Health Organization, is the subject of the WHO Opinion; and, finally, the doctrine of ultra vires acts of international organizations is, explicitly or implicitly, present in all the cases.
-  See, International Court of Justice, Reparation for Injuries Suffered in the Service of the UnitedNations, Advisory Opinion,  ICJ Rep 174, at 178-9.
-  See, J. Klabbers, An Introduction to International Institutional Law (2nd edn, Cambridge, CambridgeUniversity Press 2009), pp. 64-73; N.D. White, The Law of International Organisations (2nd edn,Manchester, Manchester University Press 2005), pp. 80-9, 98-107.
-  See  ICJ Rep 174, at 182. The Court had to answer the question whether the organization hadthe legal power to maintain its rights by bringing international claims, in this case a claim against Israelto obtain reparation in respect of the damage caused by the killing of Count Bernadotte, at that time theChief United Nations Truce Negotiator in the Middle East. The Court concluded (at 184): ‘Upon examination of the character of the functions entrusted to the Organisation and of the nature of the missionsof its agents, it becomes clear that the capacity of the Organisation to exercise a measure of functionalprotection of its agents arises by necessary intendment out of the Charter.’
-  See, arts. 4(1) and 5(1) of the Treaty on European Union. In particular after the entry into force ofthe Lisbon Treaty, the legal regime of the European Union internal and external competences is quitecomplex. See for a general treatment of the competences of the European Union, including the impliedpowers doctrine, P. Craig and G. de Burca, EU Law (5th edn, Oxford, Oxford University Press 2011),pp. 73-102; and for different aspects: L. Azoulai (ed.), The Question of Competence in the European Union,(Oxford, Oxford University Press 2014).
-  See Prosecutor v Dusko Tadic, Appeals Chamber of the International Criminal Tribunal for theFormer Yugoslavia, 2 October 1995, IT-94-1-AR72: see infra Part 3; Legal Consequences for States of theContinued Presence of South Africa in Namibia (South West Africa) Notwithstanding Security CouncilResolution 276 (1970), advisory opinion,  ICJ Rep 16: see infra Part 4.
-  Permanent Court of International Justice, Case of the SS Lotus, France v Turkey, Judgment 1927, Publ.PCIJ 1927, Series A, no. 10. The cited sentence is preceded by the following observations: ‘Internationallaw governs the relations between independent states. The rules of law binding upon States thereforeemanate from their own free will as expressed in conventions or by usages generally accepted as expressing principles of law.’