The mass movement of people across the globe constitutes a major feature of world politics today. Whatever the cause of the movement - often war, famine, economic hardship, political repression or climate change - the governments of western capitalist states see this 'torrent of people in flight' as a serious threat to their stability and the scale of this migration indicates a need for a radical re-thinking of both political theory and practice, for the sake of political, social and economic justice. This book argues that there is at present a serious gap between the legal and social practices of immigration and naturalisation in liberal democratic states and any theoretical justification for such practices that can be made within the tradition of liberal political philosophy. How can liberal states develop institutions of democratic citizenship and at the same time justifiably exclude 'outsiders' from participating in those institutions? The book examines various responses to this contradiction within the liberal tradition, and finds none of them satisfactory - there are no consistently liberal justifications for immigration control and this has serious implications both for liberal practice and theory. The first comprehensive overview of various positions within political philosophy on immigration, this original text offers a radical critique of these positions and will be of interest to students of Political Philosophy, International Relations, Social Policy and Law. Key Features: * An original contribution to political philosophy - fills a significant gap in the market * A comprehensive review and critique of theoretical arguments within political philosophy which attempt to justify practices of exclusion * An outline of a radical position on that question * A review of immigration and naturalisation practices of liberal democratic states including the USA, Canada, Europe, Australia and New Zealand * An application of the theoretical perspectives to the practices of immigration and naturalisation Winner of the North American Society for Social Philosophy's major prize - The Most Important Social Philosophy Title to be Published in 2000.