Although constitutional identity is nowadays invoked by European states primarily against the extension of the powers of the EU institutions, it can also be understood as a substantive concept of national constitutional law. This article deals with constitutional identity as a normative constitutional concept. In this respect, the problem is the same as that which arises in the relationship between EU law and domestic law: namely, its fundamental indeterminacy and the possible arbitrariness of its application. The author argues that, therefore, constitutional identity can only be plausibly invoked if satisfactory answers can be given to the questions of exactly whose identity it is, what its source is, who and how its content may define, and what the constitutional function of this category is. The second part of the study examines the Hungarian constitutional identity according to this analytical framework, and concludes that, although its subject is the Fundamental Law, its definition, content and constitutional function are unclear and contradictory. Consequently, the current concept of constitutional identity in Hungary raises a number of problems for which no plausible answers have yet been found, and it is highly doubtful whether the doctrinal and practical difficulties related to it can be resolved at all.