Once the most intriguing scholarly question in the field of political science was: what is the state? The usual answer would begin by referring to territory, borders, sovereignty, and a nation. In time the inquiry became more complex, leading to questions along the lines of: What challenges the state? How does it do so, and why? One of the responses to these questions relates to the consequences of the increasing mobility of people crossing the borders of states—both literally and metaphorically. These consequences include but are not limited to people’s access to rights and status as border-crossing noncitizens. The central normative and empirical query of this volume is in this contested domain. On the one hand, the contemporary Western nation-state preserves legally its sovereign right to determine who has the right to cross its borders as well as to exercise the political, social, and economic rights within its borders. On the other hand, rising levels of migration and increasing numbers and diversity of noncitizens within the borders of the nation-state challenge the extent to which the state may strike a balance between providing liberal, universally applicable rights and preserving its inherently distinctive identity and sovereignty.