This contribution deals with the relationship between nationality of member states and union citizenship, which was recently the object of attention in the Court of Justice, and discusses the relevant case-law. The analysis begins with the principle affirmed in the Micheletti decision (1992), even before the creation of union citizenship, according to which “it is for each Member State, having due regard to Community law, to lay down the conditions for the acquisition and loss of nationality”. It then goes on to discuss the dictum in Rottmann (2010), where the Court added that “the situation of a citizen of the Union who (…) is faced with a decision withdrawing his naturalisation, adopted by the authorities of one Member State, and placing him, after he has lost the nationality of another Member State that he originally possessed, in a position capable of causing him to lose [Union citizenship] and the rights attaching thereto falls, by reason of its nature and its consequences, within the ambit of European Union law”, and therefore “in respect of citizens of the Union, the exercise of the power [to lay down the conditions for loss of nationality], in so far as it affects the rights conferred and protected by the legal order of the Union, […] is amenable to judicial review carried out in the light of European Union law”, and can be considered legitimate if it corresponds to a reason relating to public interest and “observes the principle of proportionality so far as concerns the consequences it entails for the situation of the person concerned in the light of European Union law”. The same line of thought was repeated later in Tjebbes (2019), for cases of loss of member states nationality by operation of law entailing loss of European Union citizenship, and in JY (2022), where the Court had to deal with a decision to revoke an assurance as to the grant of the nationality of a member state, which made the loss of the status of citizen of the Union permanent for the person concerned. The argument made is that state powers regarding issues of loss of nationality are only limited by EU Law when protection of union citizenship is at stake, i.e., when there is the possibility that the status of citizen of the union will be lost (as a result of the loss of the nationality of a member state). The case-law demonstrates, thus, the interdependence of the two notions, which must also be considered in matters of acquisition of nationality, as the Court will likely have the opportunity to discuss when considering whether investor citizenship schemes comply with EU Law.