This paper focuses on the responsibility of the European Union in the context of illegal, unreported and unregulated fishing activities. It aims to debate some of the legal issues that characterize its role as a global actor dealing with marine resources and the protection of the environment. For this purpose, I analyse an Advisory Opinion of the International Tribunal for the Law of the Sea in order to describe the interplay between obligations of due diligence and attribution of conduct. Finally, I focus on international customary law possibly binding EU Member States. The paper points out the unnecessary level of complexity employed by ITLOS to establish the responsibility of the EU excluding that of its Member States and constructs a simplified form of EU responsibility applying the articles developed by the International Law Commission on the responsibility of international organizations.