What are the long-term differences in the propensity of immigrants to acquire destination country citizenship under different institutional contexts and how do these vary between migrant groups? This paper draws on micro-level longitudinal data from administrative registers in Denmark, the Netherlands, and Sweden –three countries with widely different and changing requirements for the acquisition of citizenship– to track the naturalisation propensity of eight complete migrant cohorts (1994-2001) up to twenty-one years after migration. We find that after two decades in the destination country, cumulative naturalisation rates vary remarkably with over eighty percent of migrants in Sweden, two-thirds in the Netherlands, and only around a third in Denmark having acquired citizenship. We observe lower rates and delayed naturalisation for migrants, especially among those with lower levels of education, after language requirements and integration tests were introduced in Denmark and the Netherlands. Dual citizenship acceptance in the Netherlands and Sweden, by contrast, is associated with durably higher citizenship acquisition rates, especially, among migrants from EU and highly developed countries. These findings highlight the long-term but conditional relevance of citizenship policy for immigrant naturalisation.