The book posits and develops a highly original argument about the relationship between on the one hand immigration and open borders, and on the other citizenship and nature of the polity, its democratic vitality and legitimacy. While doing so the book offers a novel approach to the work of Robert Nozick, Jürgen Habermans, John Rawls and others. The principal idea of this book is to create, at the level of political and legal theory, preconditions for the establishment of a system compatible with open borders. Open immigration policy is both the premise and the conclusion of the main argument of this book. One of the key arguments is that migration policy is fundamentally tied in with the nature and grounding of the democratic polity and its political legitimacy. This means that migration and citizenship policy cannot be reduced to evaluating costs and benefits of immigration for a given community but that it bears and depends on predominant notions of political community and legitimacy.