The study examines European Union citizenship as a distinct form of multiple citizenship that differs from the classical model of dual nationality. The paper substantiates the concept of «vertical dual citizenship», under which the nationality of a Member State serves as the basis for the emergence of supranational status, while EU citizenship, in turn, influences the limits of national regulation. It is demonstrated that this status combines a derivative nature with a tendency toward normative autonomy. Based on an analysis of the case law of the Court of Justice of the European Union (Martinez Sala, Grzelczyk, Baumbast, Rottmann, Commission v. Malta), the study reveals that EU citizenship is evolving into an independent basis for bringing individuals within the scope of Union law and into an instrument for limiting Member States’ discretion in matters of nationality. Particular attention is devoted to the development of the «genuine link» requirement and to the strengthening of the principle of proportionality in cases involving the loss of citizenship. The article concludes that EU citizenship functions as an element of multilayered legal affiliation, enabling the supranational legal order to exert reciprocal influence upon national citizenship regimes. It is argued that an integrative model is emerging in which EU citizenship acquires independent regulatory significance and transforms classical conceptions of citizenship.