Dual or multiple nationality ‘means the simultaneous possession of two or more nationalities by the same person’, according to the European Convention on Nationality of 1997,1 to which Ukraine has been a state party since 2007.2 It is generally accepted that matters of nationality—as derived from state sovereignty—fall within the domestic jurisdiction of states and form part of domaine réservé, which includes matters in which states enjoy absolute and unrestricted discretion. The determination of conditions for the granting and loss of nationality, as well as the prohibition or recognition of dual nationality, also count among these issues. However, the discretion of states likewise includes the undertaking of international obligations concerning nationality, whereby states may establish limitations on their own. The undertaking of an international obligation ‘places a restriction upon the exercise of the sovereign rights of the State’,3 although such limitations cannot be presumed.4 Therefore, the sovereignty of states and the limits set by international law on matters of nationality ‘are well compatible’ (Triepel, 1929, p. 197). The prohibition or recognition of dual nationality is governed by international law only to the extent that the state concerned undertakes international obligations pertaining to that matter.