The concept of the autonomy of EU law has received, since its inception in the 1960s, remarkably little academic attention when compared to other basic EU law premises such as “primacy” or “direct effect”, particularly from the theoretical angle. However, “autonomy” is undisputedly a fundamental and structural principle of the EU legal order. Given the reflexive nature of the term “autonomy”, to ... [Show full abstract] be distinct from something and to be able to function separately, it presupposes one or more points of reference. If these are assumed in the form of legal orders, the autonomy of EU law can be basically conceived in two ways: vis-à-vis international law or the legal systems of Member States. The concept of autonomy is traditionally perceived with regard to international law (external dimension of autonomy) as leading judgments of the Court of Justice of the EU and many of its Opinions have further developed this doctrine. This short piece attempts to clarify the meaning of the external dimension of autonomy of EU law and discuss some of the associated challenges. In this context, the paper portrays the various legal techniques and substantive requirements for preserving the external autonomy of the EU legal order from international law.