The concept of the stranger is central to the question of migration in European social and political history. In antiquity, state-building societies had strong social boundaries, and cities were very careful about who was allowed to cross the borderlines of their territory. In early modernity, after the end of the Middle Ages, the territorial state and the idea of territorial sovereignty became key factors in the management of migration of individuals—both citizens and foreigners—across borders. This paper will elucidate the concept of migration and explain its evolution in European social and political history from antiquity through the Enlightenment. The cosmopolitan concept of world citizenship is introduced as an attempt to overcome the dichotomic distinction between citizens and strangers which emerges with the territorial order of states.