Area-based initiatives are local interventions in targeted neighborhoods, typically situated within broader urban development frameworks aimed at addressing segregation. This article examines area-based initiatives as forms of social infrastructure. It draws on two cases of area-based initiatives in Nordic urban residential neighborhoods, using the concept of social infra-structuring combined with a policy arrangement framework. The study shows how a segregation discourse enrolls municipalities, housing compa-nies and civil society associations in specific ways within these arrangements. Agreements are used to formalize and enable collaboration for social issues between organizations around specific places, as a tool which interlinks space, organizations, and activities whilst providing stability albeit within a given temporality. Furthermore, the article shows civil society associations as key driving forces in enabling social infrastructuring. We argue that the requirements and expectations expressed through formal agreements of the area-based initiatives indicate an on-going professionalization of civil society. We conclude that contemporary strategies for addressing segregation through urban area development, entail a (re)configuration of the conditions for civil society associations. This suggests that social infrastructuring is not only a relational process which mobilizes civil society associations, but also one that (re)shapes their position and capacity within urban area development.