Chapter 3 explores multiple citizenship by naturalization. Naturalization rules and citizenship tests – citizenship conditionality, more generally – have been much-discussed among immigration theorists. Yet little has been said about the legitimacy of each and every naturalization requirement, taken separately. In this chapter I address two issues related to naturalization and multiple membership. First, I analyze the legitimacy of one naturalization requirement that makes a crucial difference to dual citizenship: the renunciation of previous citizenship requirement. I conclude that that requirement is morally problematic only if it is made by the state of residence instead of by the state of origin. Second, drawing on the literature on choice architecture and nudging, I develop a novel objection to dual citizenship via naturalization. I argue that what is morally problematic in such cases is that dual citizenship arises by default, rather than through an explicit individual choice. The reforms of naturalization procedures proposed in this chapter emphasize the importance of actively choosing one’s citizenship (a concern found in Chapter 2 as well).