Schmid Comparative Migration Studies (2020) 8:25 immigrants after the establishment of (long-term) residence. Hammar (1985), who popularised this distinction, further differentiates two kinds of immigrant policies. The first concerns the rights afforded to ‘denizens’ (Hammar 1990), while the second concerns citizenship policies – that is, the regulation of the access to citizenship in the sense of passport-holding or nationality. The aim of this article is to theorize, explicate, and assess this two-dimensional architecture of national boundary regimes and explore its evolution over time. I zoom in on immigration regimes and citizenship regimes to address three intertwined questions: (1) What are the main structural logics shaping immigration regimes and citizenship regimes in liberal democracies? (2) Do these two policy dimensions and the resulting two-dimensional policy space follow from these structural logics, and does this two-dimensional model withstand empirical testing? (3) What do the structural logics tell us about the trends in, the configurations of, and the correlations between immigration regimes and citizenship regimes across space and time, and can these theoretical expectations be empirically corroborated? To answer these questions, I draw on the account of Hampshire (2013) to argue that immigration policies and citizenship policies are driven by the divergent logics of markets and nations, as well as the intermediate logics of overarching liberal-constitutional and democratic institutions. Immigration policies are mainly exposed to economic and legal forces, while citizenship policies are primarily driven by democratic concerns and national identities. This structural divergence gives rise to the distinct empirical nature of immigration regimes on the one hand and citizenship regimes on the other. I further propose that each structural logic can come in a liberal or open or inclusive, or an illiberal or closed or exclusive variant. It should thus be possible to observe all four logical combinations of open or closed immigration policies and inclusive or exclusive citizenship policies. Moreover, in line with much of the existing literature that discusses this problem under the heading of the ‘gap hypothesis’ (e.g. Cornelius et al. 2014; Lutz 2019), I argue that external constraints imposed by global markets and international institutions favour open and liberal policies in the realm of immigration, while citizenship policies are less externally constrained and thus more malleable by domestic structures and political forces. This should set immigration policies on a more liberalising and convergent trajectory than citizenship policies. I then suggest that the structural logics underpinning each dimension pulls immigration regimes and citizenship regimes apart. Hence, they should not only be conceptually and statistically distinct, but also not systematically correlated. Using Categorical Principal Component Analysis (CATPCA) to scrutinize data across 23 liberal democracies from 1980 to 2010, the empirical investigation validates The National Boundary Regime Typology. The policy components of Immigration Regime Openness (IRO) and Citizenship Regime Inclusiveness (CRI) can be reduced to two internally consistent and statistically distinct dimensions. By demonstrating the empirical existence of theoretically assumed dimensions, this analysis thus addresses an important gap in the literature (Koopmans 2013: 696). There are studies that have introduced two-dimensional policy spaces of integration and citizenship regimes without testing Page 2 of 20