Citizenship combines a formal legal bond with a State and a sense of belonging to a political community—a tension made especially visible by long-term migration, which produces populations integrated in society yet often excluded from full citizenship. Naturalization is where this tension plays out, shaped by national laws that vary widely across countries. This study examines how citizenship policy relates to acquisition outcomes across eighteen European countries (former EU-15 plus Poland, Norway, and Switzerland) over 2009–2023, addressing three open questions: the temporal stability of this relationship, the role of foreign population composition, and appropriate measurement strategies. Drawing on the comparative literature and the GLOBALCIT Citizenship Law Dataset, we analyze citizenship acquisition pathways (birthright, childhood provisions, ordinary and special naturalization) across the eighteen countries, and review existing policy indices to justify our selection of the MIPEX Citizenship Indicator as the policy-output measure. Outcomes are operationalized through citizenship acquisition rates (CARs) from Eurostat data, disaggregated by age (under 20 vs 20 and over) and citizenship status (EU vs non-EU), plus a standardized rate (SCAR). OLS regressions test the policy–outcome relationship across three five-year periods (2009–2013, 2014–2018, 2019–2023) and the 2014–2023 decade, controlling for EU citizens’ share, minors’ share, and refugee impact. MIPEX significantly predicts crude CARs in 2009–2018, but explanatory power drops sharply in 2019–2023. Only in some periods is the share of EU citizens among foreigners significantly and negatively associated, and the refugee impact positively associated, with CARs. The share of minors, instead, shows no significant effect in any period. Non-EU nationals and persons under 20 consistently naturalize at higher rates than EU nationals and adults, respectively, with only a few country-specific exceptions. Standardized rates (SCAR) improve model fit over crude CARs, especially in earlier periods. Formal legal inclusiveness matters but is a time-bound, moderately powerful predictor, mediated by population composition and weakening over time—likely reflecting unmeasured factors like implementation practices and category-specific pathways. Disaggregated and standardized CARs offer more robust tools for cross-national comparison than crude naturalization rates alone.

Maria Vittoria Forte and Salvatore Strozza, Access to citizenship in selected European countries: comparative perspectives on legal regimes and intensity of acquisitions, Frontiers in Sociology: Migration and Society, 2026