Dual Citizenship in the European Union: trends and analysis (2010-2020) as stipulated in an EC Regulation can be considered ambiguous.22 Therefore, it cannot be excluded that the figures as depicted in Table 2 do not capture all persons who acquired citizenship in a particular EU Member State on the basis of modes A05-A27 in 2018. In total, the approach results in 756 possible citizenship constellations. Of these 756 constellations, 461 constellations (61%) do not restrict dual citizenship in any case. The 756 constellations covered the acquisition of citizenship of 153,317 persons for the reference year of 2018, or more than one fifth of the 672,300 citizenship acquisitions of EU citizens and nonEU citizens combined. Of these 153,317 persons, 141,669 (92.4%) were covered by a nonrestrictive citizenship constellation, meaning that dual citizenship was not restricted in any case. This shows that the majority of EU Member States mutually tolerates the occurrence of dual citizenship and that the abundant majority of EU citizens who acquired the citizenship of another member state was able to retain his or her original citizenship. In virtually all permissive states, the share of persons who acquired citizenship while being able to retain an original citizenship exceeds 90%. The single exception is the Czech Republic, where only 35.7% of persons who acquired Czech citizenship was able to do so. This is mostly caused by the relatively large number of Slovak citizens who acquired Czech citizenship in 2018 (346 out of 543 persons in total). While the Czech Republic does not restrict dual citizenship, Slovak citizenship is automatically lost upon the acquisition of a foreign citizenship (see Section 3). It is likely that a share of the persons covered by a potentially restrictive constellation in the EU-28 (11,648 persons out of 153,317 persons, or 11.6%) was still able to retain the original citizenship. As stated earlier, many important exceptions to the restrictive provisions could not be taken into account in this analysis. For example, in the Netherlands, national statistics show that the majority of EU citizens who acquired Dutch citizenship in 2018 did so on the basis of an option right.23 For seven out of eight option rights, the renunciation of the original citizenship is not required.24 It is also clear that Brexit had a substantial impact on intra-EU citizenship acquisitions, as 47,584 EU citizens acquired British citizenship in 2018, while 16,193 British citizens acquired another EU citizenship in the same year, which covers more than one third of all EU citizens who acquired another EU citizenship. Out of the 47,584 EU citizens who acquired British citizenship, 46,228 (97.2%) were covered by a permissive citizenship constellation. Out of 16,193 British citizens who acquired another EU citizenship, 14,835 persons (91.6%) were covered by such a permissive constellation. This shows that a large majority of EU citizens have been able to mitigate the personal consequences of Brexit by obtaining or retaining an EU citizenship, next to British citizenship. All in all, applying the concept of citizenship constellations on intra-EU acquisition of citizenship clearly shows the pervasiveness of dual citizenship tolerance within the European Union. It also shows that an abundant majority of EU citizens who acquired the citizenship of another EU Member State most likely became dual citizens. However, the overrepresentation of persons covered by a permissive citizenship constellation could also indicate that restrictions 22 EU Member States are required to provide statistical data on “persons having their usual residence in the territory of the Member State and having acquired during the reference year the citizenship of the Member State and having formerly held the citizenship of another Member State or a foreign or having formerly been stateless, disaggregated by age and sex, and by the former citizenship of the persons concerned and by whether the person was formerly stateless” (Art. 3 par. 1 sub d Regulation (EC) No. 862/2007). 23 CBS, Nationaliteitswijzigingen; geslacht, nationaliteit en regeling (2018) [data file], 2020, via <https://www.cbs.nl>, last accessed on 20 June 2020. 24 Art. 6A Kingdom Act on Dutch Nationality 1985. 8 RSCAS/GLOBALCIT-Comp. 2020/4 - © 2020 Author