Abstract This article is concerned with whether the concept of a legal system—long a centrepiece of state-based legal theories—is a useful conceptual tool in theorising the contemporary EU and its legal relations with its Member States. The focus lies particularly with EU directives, and with what the character and operation of this distinctive type of EU norm can tell us as regards the existence of and relations between legal systems in the EU. I argue for the view that the EU is comprised of distinct but interacting legal systems at EU and national level, and claim that the character and operation of directives supports this view. Throughout the discussion I try to bring the conceptual tools of analytical legal philosophy to bear on puzzles generated by EU law and its relations with national law, in order to show that a sound analysis of aspects of the EU can benefit from abstract legal philosophical reflection, and vice versa.