Family Matters: Modernise, Don’t Abandon, Ius Sanguinis Scott Titshaw I appreciate the ideas that Costica Dumbrava and others have introduced into this debate. States’ concerns about the quality and political consequences of their citizenship are important. But citizenship is a two-way street. Our discussion of ius sanguinis laws should extend beyond the concerns of states to also consider the serious practical consequences of citizenship laws on citizens, including the long-term unity and security of their families. Families facing instability or separation because children are denied their parents’ citizenship are unlikely to be satisfied with the explanation that ius sanguinis is inadequate or historically tainted; the resulting individual sense of injustice might even discourage the loyalty and identification states seek in citizens. This debate about citizenship transmission is necessary because of two modern changes in the facts of life: (1) increased international mobility based on cheap and easy transportation and communication; and (2) the advent and diffusion of assisted reproductive technology (ART) and new legal family forms (e.g., same-sex marriage and different-sex registered partnership). I will address each in turn. First, I’ll explain why Dumbrava’s proposal to abandon the ius sanguinis principle is an undesirable response to increased international mobility. Second, I’ll build on Dumbrava’s and Bauböck’s recognition of the inadequacy of unlimited and exclusive ius sanguinis rules for today’s families by suggesting that ius sanguinis be modernised rather than abandoned altogether. I’ll also illustrate how citizenship in federal states can add an additional layer of complexity to any universal proposal regarding citizenship. In a mobile world children need their parents’ citizenship Dumbrava’s proposal to eliminate the ius sanguinis principle would increase, rather than decrease, problems based on greater international mobility. It would eliminate one tool parents currently use for transmitting © The Author(s) 2018 R. Bauböck (ed.), Debating Transformations of National Citizenship, IMISCOE Research Series, https://doi.org/10.1007/978-3-319-92719-0_19 97