This article purports to expose the dangers of the concept of constitutional identity - a doctrine shaped by apex state courts to shield areas of the national legal systems from the influence of European law. First, the article overviews the use of the concept of constitutional identity in the case law of national and supranational courts, mapping the growing expansion of this doctrine. Second, the article seeks to reconstruct the genealogy of the concept of constitutional identity, tracing its legal origins. Third, the article advances a normative criticism of the concept of constitutional identity, explaining how the doctrine suffers from an incurable lack of determinacy, which inevitably results in arbitrariness in its use. Moreover, the article points out how the practical use of a defensive concept such as constitutional identity is poised to weaken, if not undermine tout court, the process of European integration.