Citizenship acquisition is often seen as a crucial step in the process of integrating immigrants in host societies. This paper analyzes the question why some immigrants are more likely to have acquired destination country citizenship across European states than others and tests legal-formal, socioeconomic, cultural and micro-level explanations. We use a pooled dataset of first and second generation immigrants resident in 15 European states and apply a logistic multilevel analysis to measure country of origin effects, destination country effects, as well as the effects of individual level characteristics. Our analysis shows that second generation and first generation immigrants who arrived more than 20 years ago, immigrants with one parent born in the destination country, retired workers and persons speaking the host country language at home, are more likely to become a citizen of their country of residence. Second generation Muslim immigrants are less likely to have host country citizenship than comparable non-Muslim immigrants of the second generation. Immigrants from former colonies or from poor or political instable countries are more likely to become a citizen of their country of residence. Immigrants are also more likely to have acquired citizenship in destination countries with a low net migration rate and with citizenship laws that make citizenship accessible in comparative perspective.