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.