- The present survey aims to explore the role of state practice in the context of modern international law. Not only is the process of interpretation giving concrete content to the conventional disposition, but a practice in the implementation of the treaty that go beyond the boundaries of the same, modifying it and therefore (re) acquiring a "normative" relief in the proper sense. Work on the formation of customs, on the other hand, starts in 2012 on the basis of the work of Special Rapporteur Michael Wood. In particular, these conclusions, which contains conclusions 4 to 8, refers specifically to the theme of "general practice", which must be accompanied by the acceptance as a right in order to produce the customary norm, according to the dual classic scheme. The main role for the creation of a customary rule is attributed to the practice of the States. In particular, the International Law Commission (ILC) proposes a non-exhaustive list of behaviors that can be used as a praxis, among which there is no coincidence that the practice "in connection with treaties" further proves the affinity between the two projects. The investigation phase is now also concluded with regard to the identification of the custom, and the report of the ILC of 2016 includes a commentary of these 16 Conclusions, submitted to the States at first reading. Our analysis and its purpose of this work is to identify the main hypotheses of states responsibility in connection with organizations activities, adopting the perspective of system protection established by the European Convention on Human Rights (ECHR) on which the European Court of Human Rights (ECtHR) supervises. The results to which the ECtHR has come have been extensively examined in the relevant literature. Therefore, after having reconstructed the main liability hypotheses emerged in the ECtHR jurisprudence and the critical points connected to them (section I), we will investigate new arguments to ascribe responsibility to member states on the basis of different titles, not yet explored or otherwise not still consolidated in ECtHR jurisprudence. We remain also, in the analysis of new interpretive trends with regard to the standard of proof for the attribution to the state of unequivocal conduct of liability through international jurisprudence in comparison with various courts of various statutes and different attributions that remain always under the same level of punishment for international responsibility. Final, an inductive approach, with the aim, on the one hand, of highlighting the concrete results achieved in the field of defense and peacekeeping, and, on the other, of providing possible contributions with respect to the issues raised above, in particular what the impact of international law is under the Common Security and Defense Policy and the Common Foreign and Security Policy and how it is possible to configure the responsibility of the European Union and/or the participating States to international crimes committed in the performance of the various operations. Dimitris Liakopoulos is Professor of international law, European Union law and criminal and procedural law in various Universities in US and Europe. Attorney at Law at New York and Brussels. ORCID ID: 0000-0002-1048-6468.