Part II: Bloodlines and Belonging Abstract Can the widespread legal rule of ius sanguinis, through which citizenship is transmitted at birth from parent to child, still be justified in the contemporary world? Together with addressing more traditional objections to ius sanguinis, such as its alleged ethno-nationalist character or its negative effects on the global distribution of wealth and opportunities, the debate also looks into more recent challenges to ius sanguinis, such as those posed by dramatic changes in family norms and practices and the rapid development and spread of reproductive technologies. One major worry is that current forms of ius sanguinis are unable to deal adequately with uncertainties related to the establishment of legal parentage, especially in cross-border surrogacy arrangements. Whereas most contributors agree that ius sanguinis should be reformed in order to adapt to contemporary circumstances, plenty of disagreement remains as to how this reform should be done. The debate also tackles the questions of whether and in what way ius sanguinis could be justified as a normative principle for admission to citizenship. Authors discuss important normative considerations, such as the need to prevent statelessness of children, to ensure the preservation of family life and to provide opportunities for intergenerational membership. Keywords Ius sanguinis · Citizenship · Ethno-nationalism · Reproductive technologies · Statelessness · Family law