This article aims to reconstruct and theorise the autonomy of the European Union (EU) legal system by drawing on Hartian legal theory. It comprises four claims. First, the European Court of Justice’s (ECJ) 'foundational case law' on autonomy – and direct effect and supremacy as its corollaries – is conceptualised as a second-order thesis about the genus to which EU law belongs (the 'autonomy thesis'). Second, the ECJ's reliance on the full effectiveness of EU law as a justification for the autonomy thesis alludes to the deep connection between legality and effectiveness, but this connection cannot rationally explain the normativity of the autonomy thesis as an internal statement of law. Third, in order to provide such an explanation, the autonomy thesis is reconceptualised as an 'internal recognitional statement' by which the ECJ asserts a normative formulation of an autonomous EU rule of recognition. Fourth, within this Hartian analysis of the EU legal system, the doctrines of direct effect and supremacy lack self-standing analytical value. This article finishes with some very preliminary observations on a well-known objection against the autonomy of EU law based on the attitudes and perspectivism of national courts.