'National constitutional identity' has become the new 'buzz word' in European constitutionalism over the past few years. Much has been written about the concept involving the Member States' national constitutional identities: it has been welcomed for (finally) accommodating constitutional particularities in EU law, demonised for potentially disintegrating the EU, and wielded as a 'sword' by certain constitutional courts. Scholars, judges and advocates general have rendered the concept currently so fashionable and yet so ambivalent that an in-depth analysis putting some order into the intense debate over constitutional identity is warranted. This collection brings together a series of contributions from the perspective of both scholars and judges in order to shed some light into the dark corners of constitutional identity. To this end a threefold approach has been followed: a conceptual or philosophical approach, an approach based on EU law, and an analysis of the case-law of several European courts. First the book explores what constitutional identity means and who decides on it. The next contributions analyse (and at times unveil) the areas that might collide or at least interact with constitutional identity. Among other issues the authors touch upon EU law primacy, EU citizenship as a 'hard core' in opposition to the Member States' identities, the Charter of Fundamental Rights and its Article 53, and EU criminal law and the essential functions of the State. Finally, the chapters dealing with the case-law of European courts on national constitutional identity include the perspective of various national constitutional courts, such as those of Eastern and Central European Member States, the Court of Justice of the European Union, and the much less analysed European Court of Human Rights.