This contribution discusses the construction of citizenship as a category of belonging in the newly formed multi-ethnic state of Bosnia-Herzegovina (BiH). Due to the violent conflicts between 1991–1995, ethno-national identifications are today often seen as overriding and exclusive means of defining group-membership in BiH. Whether and how citizens fill the concept of citizenship with any meaning of belonging to a state-wide community remains an open question. Drawing on fieldwork recently conducted in Mostar, I provide some tentative answers to this question. My research focuses on the process of re-unifying politico-administrative structures in this formerly divided city and closely follows interactions between international agents, citizens and various public bodies. Attributing special importance to administrative categorization practices, I argue that these constitute a source of shared experience for citizens, thus shaping their perception of what it means to be a citizen of BiH. Events in Mostar show how such a shared experience of bureaucratic categorization practices might become a powerful incentive for multiethnic collective action and a source for imagining a multiethnic, civic community. The same categorization practices might also fuel new divisive forces that diminish the internal solidarity of ethnic groups and instill new categorical divisions within the local community. I demonstrate the complexity of such processes in the case of the closely related post-war categories “refugee”, “internally displaced person” and “returnee” and conclude with some remarks on the intricacy of post-war state-building in Bosnia-Herzegovina.