Immigration shapes our evolving, interconnected world, especially in developed nations. It sparks a wide range of debates, often centered on the conditions under which immigrants are admitted and how they are integrated into society, particularly regarding policies like dual citizenship. This is significant as it affects both immigrants and the countries they move to, importantly impacting naturalization—the process by which someone not born a citizen can become one, indicating integration into their new home’s society, economy, and culture.

There is valuable research on how allowing or not allowing dual citizenship affects immigrants’ chances to naturalize. However, much of this research stops short of explaining the direct link between dual citizenship and naturalization rates, which is complex because many factors may influence migrants’ decision to naturalize, ranging from a migrant’s origin to their family condition. Also, several countries, such as Germany, are actively changing their dual citizenship laws, reflecting the dynamic nature of immigration policies and their effects on integration. Thus, understanding the effects of dual citizenship policies on immigrants’ decisions to naturalize is complex. Floris Peters and Maarten Vink address this complexity in their insightful APSR letter, examining how these policies influence naturalization rates in Sweden and the Netherlands.

Sweden and the Netherlands provide valuable case studies because of their developed welfare systems, free movement within the EU that attracts many immigrants worldwide, and the availability of comprehensive data. Sweden’s policy allowed immigrants to retain their original citizenship, while the Netherlands reversed its liberalized citizenship policy, requiring immigrants to give up theirs unless married to Dutch citizens. Besides its comparative design, Peters and Vink’s study is groundbreaking for its “quasi-experimental approach” to understanding the causal effect of changes in dual citizenship law. Since having dual citizenship depends on the laws of two countries of migrants, they argue, immigrants whose origin countries do not allow dual citizenship anyway will not be affected by the changes in the laws in the destination countries. Hence migrants from these countries can be used as a “control group” (which is not affected by the changes in Sweden and the Netherlands), whereas migrants from countries that do allow dual citizenship are part of the “treatment group” (which is affected by the liberalization/restriction). They use information on citizenship legislation from 200 migrant-origin countries to identify which migrants are affected by the policy changes in the two countries, and which migrants are not, examining changes in naturalization rates before and after policy adjustments. This approach presents clearer insights into how these laws affect immigrants’ decisions to fully become part of their new societies.

The authors’ findings show crucial impacts, highlighting that leaving the renunciation requirement in Sweden increased naturalization rates by 6.7%, while reintroducing it in the Netherlands decreased rates by 6.4%. These findings present the important influence of dual citizenship policies, particularly among immigrants from less developed or non-EU countries, who are more inclined to integrate into their new countries. The selection of Sweden and the Netherlands for their study is significant because of the comparable legal requirements for citizenship in both countries during the observation periods surrounding their respective reforms. This similarity permits a more precise examination of dual citizenship policies’ effects.

Using detailed administrative records to follow legal foreign-born residents, Peters and Vink confirm that not all immigrants are equally impacted by dual citizenship policies because of varying national regulations on renouncing citizenship. Their research highlights the importance of maintaining one’s original citizenship, especially for individuals from the EU or wealthier countries, and the complex considerations involved in belonging to a new nation, presenting a nuanced understanding of the association between dual citizenship, naturalization, and integration. Their research contributes to scholarly discussions and provides valuable insights for policymakers, advocating for more inclusive and effective immigration policies. This study bridges the gap between theory and practice, supporting our understanding of citizenship in a globalized context. ■

PETERS, FLORIS, and MAARTEN VINK. 2023. “Heterogeneous Naturalization Effects of Dual Citizenship Reform in Migrant Destinations: Quasi-Experimental Evidence from Europe.” American Political Science Review: 1–8. https://doi.org/10.1017/S0003055423001193.