Luuk van der Baaren 1.1.1 Requirement to renounce the original citizenship upon the acquisition of citizenship (Globalcit modes of acquisition A05-A27) From a receiving state perspective, countries can restrict dual citizenship by compelling a person to renounce his or her original citizenship upon acquisition of citizenship. This often requires explicit renunciation of the original citizenship, which can usually be achieved by making a declaration. In a number of states, citizens can only be released from their citizenship with the prior approval of the public authorities. Next to that, additional conditions can apply, for example that military service must have been completed prior to the renunciation of citizenship. The practical ramifications of a renunciation requirement depend on the citizenship law of the origin state, and the receiving state’s interpretation thereof. Firstly, if the original citizenship is automatically lost upon the acquisition of another citizenship, the requirement to renounce the original citizenship might be considered redundant.10 Conversely, a number of countries still adhere to the doctrine of perpetual allegiance, meaning that the citizenship of the origin country cannot be renounced at all.11 In addition to that, the renunciation of the original citizenship cannot be reasonably required in certain cases, for example if renunciation is excessively costly or if it would lead to the loss of property rights in the origin state. In such cases, persons are commonly exempted from the renunciation requirement, as stipulated by Art. 16 of the European Convention on Nationality.12 As the precise conditions for these exceptions are often complex and can usually only be retrieved from subsidiary legislation or administrative guidelines, these will not be further discussed in the analysis. 1.1.2 Loss of citizenship upon the acquisition of a foreign citizenship (L05) From a sending state perspective, countries can restrict dual citizenship by revoking citizenship of a citizen who acquires a foreign citizenship. The revocation of citizenship either takes place automatically when another citizenship is acquired or can alternatively be withdrawn, meaning that an act of the public authorities is required in order to initiate the loss of citizenship. 1.1.3 Loss of citizenship upon retention of a foreign citizenship (L06) Dual citizenship regularly arises during childhood, for example if parents transmit more than one citizenship iure sanguinis, if citizenship is acquired iure sanguinis as well as iure soli. In countries where dual citizenship is restricted, persons can therefore be required to renounce their other citizenship(s) before attaining a certain age, as they might otherwise lose their citizenship. In Table 1, an overview is provided of the above-mentioned modes of acquisition and loss in 28 EU Member States for the reference date of 1 January 2020. The data is drawn from C-192/99, Kaur, par. 19; Case C-200/02, Zhu and Chen, par. 37; Case C-135/08, Case C-34/09, Zambrano, par. 42. Rottmann, par. 59; Case C-221/17, Tjebbes, par. 48. 10 For an overview of countries where this is the case, see: Vink, M. et al., (n 2). 11 Ibid. 12 On 1 January 2020, the European Convention on Nationality had been signed and ratified by 13 EU Member States (Austria, Bulgaria, Czech Republic, Denmark, Finland, Germany, Hungary, Luxembourg, Netherlands, Portugal, Slovak Republic and Sweden), albeit in certain cases with reservations. See: <https://www.coe.int/en/web/conventions/full-list/-/conventions/treaty/166/signatures?p_auth=ORav5mQp>, last accessed on 20 June 2020. For a further analysis, see: De Groot, G.R., The European Convention on Nationality: a step towards a ius commune in the field of nationality law, Maastricht journal of European and comparative law, Vol. 7, No. 2, 2000. RSCAS/GLOBALCIT-Comp. 2020/4 - © 2020 Authors 3