‘Constitutional identity’ has become a key argument in the negotiation of authority between national legal orders and the legal order of the European Union. Many national constitutional courts have declared that the reach of EU law is limited by certain core elements of the national constitution, often labelled ‘constitutional identity’. However, the rise of ‘illiberal democracies’ within the European Union, especially exemplified by the democratic backsliding of Hungary and Poland, has put constitutional identity into a questionable spotlight. Both countries have been leaning on the constitutional identity to both erode European legality and defend their authoritarian constitutional projects againstEuropean criticism. This dissertation deals with the question of how to delimit legitimate invocations of constitutional identity from abuses of constitutional identity. It develops a typology of constitutional identity abuse in three dimensions: The generative, the substantive, and the relational. The generative dimension is concerned with how a constitutional identity claim has come about, its relation to constituent power, constitutional enactment and amendment, the independence of courts, and the regulation of historical memory. The substantive dimension deals with what a constitutional identity claim entails, digging into the normative expectations invoked by the concept and the ways in which it ought to be regarded as intertwined with and embedded in a normative conception of constitutionalism. Finally, the relational dimension is concerned with how a constitutional identity claim is advanced. Advancing a constitutional identity claim in the European legal space evokes notions of diversity, dialogue, recognition, and pluralism, which need to be reciprocated. In each of these dimensions, ways in which constitutional identity can be abused will be identified, using Europe’s ‘backsliding democracies’ Hungary and Poland as the primary case studies, while discussing other countries where appropriate.