The principle of autonomy is the outcome of judicial invention. It was read into primary law by the Euro- pean Court of Justice in order to enable EU law to withstand challenges from national law. Since the early 1990s, however, an external dimension of the principle has emerged clearly and, at times, forcefully. This is about protecting the distinct characteristics of the mature EU legal order from interferences origi- nating beyond the Union. Autonomy is now associ- ated with controversial episodes in the interactions between EU and international law (for instance, Mox Plant and Kadi and, more recently, Opinion 2/13).