Since 1998, several European countries have attached obligatory civic integration requirements to the process of becoming a citizen, which include language proficiency, country knowledge, and value commitments. Why have some European states adopted new membership criteria while others have not? In this study, I make the argument that civic integration requirements are a response to both real and popular pressures of immigration. In explaining civic integration policy change, I emphasize three conditions in which these pressures manifest: (1) prior experience with immigration; (2) a high number of non-European foreign residents today; and (3) public/electoral pressure to "do something" about immigration and diversity-related problems. In response to these historical and contemporary factors, political elites implement civic integration requirements with the dual goal of promoting integration and controlling immigration.

In order to explain new membership requirements, I first develop measures to systematically identify and compare civic integration policies across cases and time. I construct an original index—the Civic Integration Policy Index (CIVIX)—for measuring and comparing these changes in the "EU-15" over a ten-year period (1997-2007). This study also uses a combination of cross-national, medium-n analysis with a single case examination of Great Britain to show where and how real and popular pressures of immigrant-related diversity matter for adopting new membership requirements. This study draw on extensive in-depth interviews conducted in 2006 and 2007 with high-level policymakers and elected officials.

As a result of new civic integration requirements, the institution of citizenship in liberal democracies is undergoing fundamental transformation. New requirements balance out previous liberalization of citizenship policy that has given more people access to citizenship without accompanying obligations of membership. Requirements also infuse new content into traditional national membership, emphasizing a universal not particularistic set of skills and values. Finally, civic integration requirements modify citizenship from an exclusionary device to an instrument of inclusion. In the context of continued mass migration and globalization, these transformations make national citizenship more relevant now than ever before.