This article introduces the concept of the internal border and explores how it operates within urban spaces. The internal border refers to the shift from the external line of the state's territory toward diverse sites and actors within the state. It highlights the border's turn to the city and urban space, which is connected to the external border. The internal border is 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. The border articulates social differences mapped onto space, creating the dividing line between insiders and outsiders, citizens and non-citizens, and the growing number of fine-tuned categories of non-citizens, along with divisions of racialisation and ethnicisation, class, gender, sexuality, and health. The internal border is a symbolic distinction that speaks to the border within society, even when operated from afar as part of colonial rule. It is defined as conceptual distinctions made by social actors to categorise objects, practices, and people, while social boundaries are the objectified forms of social differences manifested in unequal access to and unequal distribution of resources. Boundaries thus reflect the symbolic frontier between groups. The internal border is not a fixed territorial line but a socio-political and cultural practice that constitutes and represents differences in space. The internal border is a mechanism of differentiation and exclusion that operates both inside and outside the territory of a given state or city. It includes the filtering and selection of those requesting entry, the allocation of different statuses to those who enter, and the selective, partial, and fragmented inclusion of those territorially present, together with their detention and deportation, or its threat. The boundaries between the external, international, and urban/local borders are blurred. The Special Issue explores how the city is connected to the border and how the city is a site of bordering. It advocates for a multiscalar and relational framework to scrutinise the role of the city, coupled with the constructivist notion of the border as a space of negotiation. The city is understood as a space of a multiplicity of social groups and actors who operate within a multiscalar setting of legal frameworks and everyday practices on urban, regional, national, supranational, and transnational scales. The Special Issue also highlights the role of the city in the production of the border and the politics of exclusion, where state and non-state actors, from urban and other scales as well as ordinary citizens, engage in bordering. The contributions of this collection show how the internal border is made and unmade, how different migrant groups are included into or excluded from different social fields, and how the internal and external border controls are intertwined. The Special Issue also explores how the border emerges in urban space and how the internal border is shaped by intersecting categorisations of "race" and ethnicity, class, gender, sexuality, and health status.This article introduces the concept of the internal border and explores how it operates within urban spaces. The internal border refers to the shift from the external line of the state's territory toward diverse sites and actors within the state. It highlights the border's turn to the city and urban space, which is connected to the external border. The internal border is 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. The border articulates social differences mapped onto space, creating the dividing line between insiders and outsiders, citizens and non-citizens, and the growing number of fine-tuned categories of non-citizens, along with divisions of racialisation and ethnicisation, class, gender, sexuality, and health. The internal border is a symbolic distinction that speaks to the border within society, even when operated from afar as part of colonial rule. It is defined as conceptual distinctions made by social actors to categorise objects, practices, and people, while social boundaries are the objectified forms of social differences manifested in unequal access to and unequal distribution of resources. Boundaries thus reflect the symbolic frontier between groups. The internal border is not a fixed territorial line but a socio-political and cultural practice that constitutes and represents differences in space. The internal border is a mechanism of differentiation and exclusion that operates both inside and outside the territory of a given state or city. It includes the filtering and selection of those requesting entry, the allocation of different statuses to those who enter, and the selective, partial, and fragmented inclusion of those territorially present, together with their detention and deportation, or its threat. The boundaries between the external, international, and urban/local borders are blurred. The Special Issue explores how the city is connected to the border and how the city is a site of bordering. It advocates for a multiscalar and relational framework to scrutinise the role of the city, coupled with the constructivist notion of the border as a space of negotiation. The city is understood as a space of a multiplicity of social groups and actors who operate within a multiscalar setting of legal frameworks and everyday practices on urban, regional, national, supranational, and transnational scales. The Special Issue also highlights the role of the city in the production of the border and the politics of exclusion, where state and non-state actors, from urban and other scales as well as ordinary citizens, engage in bordering. The contributions of this collection show how the internal border is made and unmade, how different migrant groups are included into or excluded from different social fields, and how the internal and external border controls are intertwined. The Special Issue also explores how the border emerges in urban space and how the internal border is shaped by intersecting categorisations of "race" and ethnicity, class, gender, sexuality, and health status.