When is the EU responsible under international law? Is the EU a 'special case' international organisation? The UN General Assembly's adoption of the ILC articles on the International Responsibility of International Organizations was only the catalyst for debate on this topic. In this book, the author examines the legal personality of the EU, how - if at all - its responsibility under international agreements is shared between Member States, and how the international responsibility of the EU relates to its internal responsibilities under EU law. By exploring how in practice such legal regimes as the ILC, UNCLOS, and the WTO have held the EU responsible, this book provides an innovative analysis of a fundamental aspect of the relationship between the EU and international law.