This article examines the development and particular nature of the rule of law in the European Union against the background of the wider legal and political theoretical debate on the principle. It hence analyses the case law of the Court of Justice of the EU and the Treaty revisions on the rule of law. It argues that the principle has developed greatly since the first mention of it in the case law of the Court and contends that the principle has a particular focus in the EU on judicial protection in light of human rights. Nonetheless it is hard to apply the dichotomies running through the debates in legal and political theory to the development of the principle in the EU; an idiosyncratic mix of features seems to emerge. Moreover, this article also takes the case study of the external dimension of migration control to assess the current challenges to the rule of law in the EU. It thereby uncovers ways of working in the EU that are hard to reconcile with the rule of law requirements.