This book aims to address treaty conflict in international law, and to illuminate in particular the situation with respect to the EU. The relationship between international law and EU law is a source of great confusion, yet is, despite its importance, analysed and discussed only relatively rarely. The present monograph (or ‘duograph’, if you will) aims to contribute to the study of this relationship by concentrating on one small, highly specialised, aspect thereof: the relationship between obligations arising under treaties concluded by EU member states, and those member states' obligations under EU law.

The interest is this: treaties are, under general international law, binding upon the parties to them, and not capable of creating rights or obligations for third parties. Should conflicting treaties be concluded, either by design or – more likely perhaps – as a result of ignorance, then ideally a conflict rule kicks in. International law does indeed have such a conflict rule; in fact, it has several, but none of these seems to work to great satisfaction. The EU has its own conflict rule as well, one which appears at first sight to be rather generous towards international law and which is often indeed held to be so. Yet, its scope is limited: it applies only to treaties concluded by member states before they joined the EU (and, as we shall see, the Court of Justice has been less than fully generous in its interpretation).