<p>European Union citizenship was established by the Treaty of Maastricht in 1992. Intended to fall within the exclusive prerogative of the Member States, it soon became clear that the autonomy of Member States to determine matters relating to nationality would be restricted by the ever-expansive reach of the European Court of Justice. As such, the European Court of Justice transformed the law on citizenship in the 2010 case of Rottmann where measures affecting or depriving the rights conferred and protected by the European Union were held to fall within the scope ratione materiae of European Union law. While Rottmann affirmed the law as to the deprivation of European Union citizenship, it left unanswered the question whether the acquisition of nationality also falls within the scope of European Union law. This paper aims to identify and analyse the law arising post-Rottmann to determine whether the acquisition of nationality could fall within the scope of European Union law. It shall then analyse whether fundamental principles of European Union law, namely the principle of proportionality, could be applied in order to regulate the conditions imposed by Member States in relation to the acquisition of nationality.</p>