First published online: 20 July 2020In this article, I introduce a typology that maps the regulation of two fundamental boundaries of modern nation-states regarding immigration: territorial boundaries and membership boundaries. Based on a theory of the structural logics underlying Immigration Regime Openness (IRO) and Citizenship Regime Inclusiveness (CRI), I make four observations on the two-dimensional policy space determined by the relative porousness of these two boundaries. First, a Categorical Principal Component Analysis (CATPCA) using a combination of original and existing panel data across 23 liberal democracies from 1980 to 2010 confirms that IRO and CRI are internally consistent and statistically distinct dimensions. Immigration ...