Dual Citizenship in the European Union: trends and analysis (2010-2020) EEA- and NATO Member States, as well as Australia, Brazil and New Zealand, in addition to a range of smaller exemptions. Another finding is that dual citizenship is restricted asymmetrically in five EU Member States. In Bulgaria, Croatia and Slovenia, dual citizenship is restricted for foreign citizens who acquire citizenship, but not for citizens who acquire a foreign citizenship. Conversely, in Ireland (for citizens by naturalisation) and Slovakia, dual citizenship is restricted for persons who acquire a foreign citizenship, but not for foreign citizens who acquire citizenship. Dual citizenship can only occur if two states concurrently permit dual citizenship. Therefore, this report has also studied provisions requiring the renunciation of the original citizenship for acquisition of citizenship and provisions imposing the loss of original citizenship upon acquisition of a foreign citizenship in cohesion, or as ‘citizenship constellations’. In total, this 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. Of these 153,317 persons, 141,669 persons (92.4%) were covered by a non-restrictive citizenship constellation, meaning that dual citizenship was not restricted in any case. 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. 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%) was 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. However, the overrepresentation of persons covered by a permissive citizenship constellation could also indicate that restrictions on dual citizenship impede persons from acquiring another EU citizenship. This possibility can be further assessed on the basis of the naturalisation rate. An analysis of the naturalisation rates of citizens of EU Member States in the United Kingdom as well as British citizens in EU Member States indeed indicates that naturalisation rates are far lower for restrictive constellations than for permissive constellations. Between 1 January 2010 and 1 January 2020, nine EU Member States (Austria, Bulgaria, Czech Republic, Denmark, Germany, Latvia, the Netherlands, Slovakia and Spain) enacted changes in their citizenship legislation related to dual citizenship. In all except two countries (the Netherlands and Slovakia), these changes embodied a further tolerance of dual citizenship. Two countries (Czech Republic and Denmark) abolished dual citizenship restrictions altogether, while the remaining countries introduced new exception grounds to their dual citizenship restrictions. In certain cases, these changes introduced broad exception grounds, such as exceptions regarding citizens of particular states (Bulgaria and Latvia) or spouses of citizens (Bulgaria), or exceptions regarding the ‘option duty’ for those who established sufficient ties with the country during minority (Germany). In other countries, changes were smaller in scope, such as the introduction or the broadening of a distinct route to citizenship without a requirement to renounce the original citizenship for the victims of National Socialism (Austria), the descendants of Sephardic Jews (Spain) or investors (Bulgaria). These developments again underline the increasing tolerance of dual citizenship. The further proliferation of grounds for exemption from dual citizenship restrictions shows that restrictive states increasingly mitigate their resistance to dual citizenship, but also that dual 18 RSCAS/GLOBALCIT-Comp. 2020/4 - © 2020 Author