The assumption that international organizations can indeed carry obligations under international law (see Section 6), inevitably begs the question whether their international responsibility could also be engaged. For such responsibility to be engaged, two requirements have to be satisfied: (1) the international organization has to commit an internationally wrongful act, that is it has to violate an international obligation it possesses; and (2) this wrongful act has to be attributable to it. The International Law Commission (ILC) has made a commendable effort to draw up rules governing the responsibility of international organizations, modelled on its earlier Draft Articles on Responsibility of States for Internationally Wrongful Acts:1 the Articles on the Responsibility of International Organizations  (AIRO). This document is not free of controversy; notably, it is doubtful whether all its provisions are truly a codification of existing law. Still, the ARIO have set the terms of the debate. Some of its provisions have already been applied by courts. This process that may fuel the ARIO’s legitimacy.
One of the most fascinating issues pertaining to the responsibility of international organizations concerns the delimitation of the responsibility of the international organization and its member states. Most international organizations have separate legal personality (see Section 1), as a consequence of which ordinarily their own—and not their member states’—responsibility will be engaged for wrongful acts of their making. In some circumstances, however, international organization conduct is not entirely isolated from the conduct of member states, for example, where a member state aids, controls, or coerces an international organization (cf. arts. 58-60, AIRO), or vice versa (arts. 14-16 ARIO). In such cases, member states’ responsibility could be engaged, possibly alongside the international organizations’ responsibility.
Almost all judicial decisions that are relevant to international organization responsibility concern exactly the issue of the responsibility of member states for acts carried out in the framework of, or in connection with, international institutional action. This comes as no surprise, as dispute-settlement mechanisms do not normally have jurisdiction over international organizations, or at least do not have the competence to establish their international responsibility. Mechanisms such as the International Court of Justice, the European Court of Human Rights, and domestic courts do have jurisdiction over states, however. This explains why aggrieved individuals or legal persons have tended to bring claims against member states in such fora, even if the involvement of the member state in the impugned international organization act was rather tenuous.
Early court cases with respect to the delimitation of the responsibility of international organizations and their member states revolved around private liability rather than international responsibility questions. For example, in Westland Helicopters, a private corporation asked courts to hold member states liable for the debts of the defunct Arab Organization for Industrialization (Westland Helicopters I and II, Ahlborn). A similar scenario played out in the litigation initiated by various creditors against member states of the collapsed International Tin Council. In these cases, courts did not reach unisonous verdicts: some courts dismissed the cases on the ground that an international organization has a separate legal personality, while others were willing to pierce the organizational veil and hold the member states responsible.
Later cases mainly related to the delimitation of international responsibility between the international organization and its member states with respect to human rights violations. A substantial number of these cases concern the allocation of responsibility for such violations committed in the framework of international military operations. In these cases, however, courts were not so much called on to decide whether member states were responsible for violations committed by, or liabilities incurred by the international organization. Rather, they had to decide whether the impugned act should be attributed to the troop-contributing state whose service-members committed the act, or instead to the international organization (often the UN) under whose auspices the military operation unfolded. This situation is governed by arts. 6 and 7 ARIO. While initially the European Court of Human Rights (ECtHR) took the view that in such cases the exercise of ‘ultimate control and authority’ would be the yardstick (Behrami, Villalpando), in more recent cases, courts, including the ECtHR, have applied an ‘effective operational control’ standard (Mustafic and Nuhanovic, Spijkers; Mukeshimana, Ryngaert; Al Jedda, Sari). The latter standard is more in line with what the ILC had in mind for military operations; effectively, some of these decisions refer to the ARIO. It bears notice that the ECtHR has at times avoided dealing with the apportionment of responsibility between member states and the international organization, by holding that the applicants did not fall within the jurisdiction of the member state in the first place (Bankovic, Scovazzi).
Another line of cases decided by the ECtHR addresses the responsibility of a member state for human rights violations which were committed by an international organization, but, to some extent, involved the state. The locus classicus is the implementation of a binding sanctions regime, enacted at the level of the international organization, but implemented by its member states. The ECtHR has held that individuals who claimed that the sanctions regime breached their human rights did fall within the jurisdiction of the member state implementing the international organization sanctions. Nevertheless, the member state’s responsibility would only be engaged in cases where the international organization does not provide human rights protection in a manner that is at least equivalent to the protection granted by the ECHR (Bosphorus, Lock). Under the Bosphorus principle, a member state’s responsibility risks being engaged by the mere transfer of competences to an international organization which fails to adequately protect human rights, provided that an intervening action of the state could be proved. In later cases, this state action was relaxed to the point of even disappearing (Gasparini, Lock). In practice, however, in spite of a responsibility net that is prima facie cast wide, the ECtHR has never actually held a member state responsible for a wrongful act committed by an international organization under this principle. In contrast, responsibility has been found where the member state exercised discretion when acting in the context of international organization activity, for example, where it enters into a constitutive agreement that is violative of human rights (Matthews, Barros), or where it goes beyond the mere implementation of international organization obligations.
Case-law on the responsibility of international organizations remains in a state of flux. To be true, it is hardly contested that the responsibility of international organizations, just like the responsibility of states, can be engaged. Similarly, as far as the relationship between member states and international organizations is concerned, it is widely accepted that membership alone does not suffice to hold member states responsible for the acts of international organizations to which they have transferred competences. It remains unclear, however, under what precise circumstances member states’ responsibility could nonetheless be engaged. For instance, could they be held responsible on the basis that they have ‘circumvented’ their international obligations by transferring competences to international organizations; and if so, what would precisely count as circumvention? (cf. art. 61 ARIO). Could they be held responsible on the ground that they ‘abused’ the legal personality of international organizations? Even where agreement seems to have been reached on an applicable standard, for example, the effective control standard with respect to the apportionment of responsibility in military operations, the exact operational parameters may remain elusive. Given the dearth of state and institutional practice regarding the contours of international organization responsibility, courts will be key actors in developing this legal category. The thickening case-law with respect to the apportionment of international responsibility in international military operations is a harbinger of more to come.
-  Adopted November 2001 (Supplement No. 10 (A/56/10), ch. IV.E.1.
-  Adopted 9 December 2011 a/62/10.
-  cf. Supreme Court of The Netherlands, 6 September 2013, ECLI NL:HR:2013:BZ9225 (Nuhanovicv The Netherlands); Supreme Court of The Netherlands, 6 September 2013, ECLI NL:HR:2013:BZ9228(Mustafic c.s. v The Netherlands).
-  The International Tin Council Case, JH Rayner (Mincing Lane) Ltd v Department of Trade andIndustry  3 WLR 969 (CA),  2 AC 418 (HL),  3 All ER 523,  BCLC 102. ReInternational Tin Council, Maclaine Watson v International Tin Council  Ch 419,  2 WLR1229,  1 All ER 890. Re International Tin Council, Judgment, Maclaine Watson v International TinCouncil  3 WLR 1159 (CA).
-  Pursuant to art. 6.1 ARIO, ‘[t]he conduct of an organ or agent of an international organizationin the performance of functions of that organ or agent shall be considered an act of that organizationunder international law, whatever position the organ or agent holds in respect of the organization.’ Underart. 7 ARIO, ‘[t]he conduct of an organ of a State or an organ or agent of an international organization thatis placed at the disposal of another international organization shall be considered under international lawan act of the latter organization if the organization exercises effective control over that conduct.’
-  For example M.S.S. v Greece and Belgium (2011) ECHR 2011.
-  cf. Institut De Droit International, ‘The Legal Consequences for Member States of the Nonfulfilment by International Organizations of their Obligations toward Third Parties’, resolution adopted1 September 1995 (Lisbon 1995).
-  cf. Jean d’Aspremont, ‘Abuse of the Legal Personality of International Organizations and theResponsibility of Member States’ (2007) 4 International Organizations Law Review 91.
-  In Mothers of Srebrenica, for instance, The Hague District Court held rather controversially, in a2014 decision, that The Netherlands had effective control over a situation on the ground that Dutch soldiers acted ultra vires the orders of the UN commander. Court of Appeal ‘s-Gravenhage 30 March 2010,LJN BL8979 (Mothers of Srebrenica v The Netherlands).