Liberal democracies face increasing political polarization and are witnessing the rise of post-liberal authoritarians who challenge arguments for the justice of open borders. For instance, scholars such as Joseph Carens argue that according to their own liberal democratic values, many North American and European countries that restrict access to citizenship to foreigners are indefensible and need reform. Going further, Arash Abizadeh argues that open borders and the denial of state sovereignty are necessary to secure human rights; freedom of movement across borders is a basic human right and necessary to reduce global poverty and inequality. Looking to classical political philosophy, scholars such as Rebecca LeMoine argue that openness to strangers is not simply just to foreigners but also allows for the flourishing of citizens. Far from exhibiting hostility to foreigners, Plato’s dialogues reveal that foreigners play a role similar to that of Socrates: the role of gadfly. This volume examines these themes and fundamental questions of indigeneity, migration, cultural diversity, and the rights of foreigners in the history of political thought.