The analysis in the preceding chapters has covered a wide range of territory, spanning the twenty-seven countries of the European Union. It has shown the tremendous diversity in the ways in which EU countries attribute citizenship – defined in a legal sense, as membership in a national political community – highlighting the changes that have taken place over time, particularly in the past two decades.

The basis for much of the cross-national and over-time analysis in the book stems from the Citizenship Policy Index (CPI), a clear and systematic instrument (introduced in Chapter 1) for measuring and comparing citizenship policies. By applying the CPI to the EU-15 in both the 1980s and 2007, I was able to explore two social science “puzzles” that emerged from the results, in relation to both historical variation (addressed in Chapter 2) and more recent continuity and change (developed cross-nationally in Chapter 3, then fleshed out by case studies in Chapters 4–6). And it provided a baseline and framework for exploring the politics of citizenship in the four historically liberal countries (in Chapter 7), as well as in the twelve most recent EU member-states (in Chapter 8).

Although certainly not a fully comprehensive measure, the CPI condenses the extraordinary complexity of citizenship laws into a common and meaningful lens through which to analyze and compare policies across time and space. Without the systematic comparisons from this “medium-N” analysis, it would be difficult to make broader arguments that are coherent and persuasive.