Relations among mobile people sharing the same cultural identification are often tension-ridden. In this doctoral thesis, I explain the relation between mobile people’s social differentiation and their efforts to generate capital in in-group relations, in local contexts as well as in transnational social fields. Drawing on migration studies as well as on social differentiation research, I combine the boundary-approach with a Bourdieu-based understanding of transnational migrants’ strategies of capital accumulation. The approach I introduce thus reveals the interconnection of dynamics in local and transnational social fields. The interest of the case study, Hamburg-based people identifying as Iranians, lies in a century-long history of migration, the contemporary social, cultural, economic and political importance of the port city as a destination for Iranians, and the relevance of the German case in the current debate on immigration. The fine-grained ethnography of in-group relations offers detailed insights into migrants’ capacities to juggle resources from the past and the present, and between the local and the transnational. Practices of boundary-making emerge as a form of competitive engagement with the conditions of capital accumulation specific to social fields that are shaped by diverse regimes of value. More generally, the study attests to the fluidity and relativity of social differentiation while also demonstrating the pervasiveness of value regimes that prioritize resources identified as Western throughout space and time.