In Van Gend en Loos and Costa, the Court stated that EU law was an autonomous legal order which limited the sovereignty of member States. These EU law qualities prevent other laws determining central elements of EU law (‘autonomy of EU law’); grant precedence to EU law over national law (‘primacy of EU law’); allow EU law alone to determine when there is a conflict between it and national law and the consequences of that (‘pre-emption’); and require national authorities to ensure that the EU legal system functions effectively and its authority is sustained (‘fidelity principle’). Historically, most national courts have accepted the authority of EU law over national law, subject to three constraints. First, EU law should not violate fundamental rights recognised in their respective constitutions. Secondly, if it generates significant consequences for the national democracy, the EU law must not be clearly ultra vires. Thirdly, a number of courts will not accept EU law primacy on matters that go to that State’s constitutional identity, most notably those issues over which that court believes national parliaments have the necessary democratic pedigree.

On the face of it, from the perspective of some orthodox EU lawyers, constitutional identity may sound like another open-ended limit to EU integration – and a limit of the worst kind. Admittedly, if over-extensively relied on and construed in a very conservative manner, identity can be a powerful weapon in the hands of constitutional court justices who would somehow transfer warfare between Member States from actual frontlines to judicial terrain. Yet this chapter argues that there are not only – or perhaps even mainly – vices attached to national constitutional identity, at least in the French approach. As long as it is used wisely, that concept may indeed have several virtuous effects at the systemic and also the substantive level. It is ultimately for the alchemists of constitutional identity (that is, constitutional courts, in conjunction with the Court of Justice of the European Union) to decide to make of that concept either a bridge between legal orders, a porous boundary, or a thick and high wall.