ABSTRACT This editorial to the Special Issue introduces the concept of the internal border and presents its individual contributions. It discusses the shift from the borderline toward diverse sites and actors within the territory of the state and points to the border’s still neglected turn to city and urban space, and how this is connected to the external border. In doing so, the introduction explores the meanings of the internal border as a crucial mechanism of ordering and othering that represents, enacts, and creates the line between insiders and outsiders, citizens and non-citizens, along with divisions of racialisation, ethnicity, gender, class, and health. This notion assumes that the practices of bordering articulate social differences mapped onto space. Thus, recognizing the city as urban border space, this introduction proposes studying the border through the city, embedded within a multiscalar and relational framework.