Joint and several liability of States/international organizations under international law - A neglected institution

International responsibility, i.e. the set of secondary obligations of cessation, non-repetition and reparation of subjects of international law, i.e. States and international organizations, for violations of primary obligations of international law that can be attributed to them, is distinct and divisive. In principle, each responsible State and/or international organization can be sued individually (and not jointly with others), and must answer for the breach of its international obligations only up to the amount of its contribution to the injury caused (and not the entirety of the injury). The difficulty lies in the fact that violations of international law are increasingly committed by several States and/or international organizations. This is particularly true of violations of international human rights law. Concurrence or plurality of responsibility exists when several States and/or international organizations contribute to the violation of the rights of the same persons, and thus to the same damage - whether or not these violations relate to the same obligations and give rise to the same wrongful act. We shall mention three constellations in which these plural or shared responsibilities for violations of international human rights law can be observed: (i) transnational interventions by certain States and/or international organizations which lead them to exercise jurisdiction over human rights holders outside their territory (e.g. in the case of occupation or peacekeeping missions); (ii) transnational movements (physical or virtual) of human rights holders themselves which bring them under the jurisdiction of several States and/or international organizations (e.g. in the case of migration, deportation, trafficking or cyber-surveillance) ; and, finally, (iii) transnational cooperation between several States and/or international organizations, which makes their rights and activities, even national or internal, interdependent (e.g. in the case of EU migration or monetary policy, or international mutual legal assistance).