Transnational social spaces denote the circular flow of persons, goods, information and symbols across countries that have been triggered in the course of international labor migration and refugee flows. The question is how such transnational phenomena can be described, catagorued and explained. What are the implications for the adaptation of international migrants and their descendants in the economic, political and cultural realms in the countries of setdement? First, this discussion clarifies basic concepts, such as transnational social space and the main resources involved, such as various forms of social capital, the norm of reciprocity, solidarity, information and control. Second, the analysis outlines some causal macro-factors that may have opened up opportunities for migrants to build transnational spaces to a greater extent than before World War Two. Third, a few forays into the empirical realm serve to sketch the lineaments of the German-Turkish transnational social spaces: the emergence of Turkish niche businesses in Germany and transnational businesses spanning both countries; efforts of some Kurdish organizations to establish a homeland called ‘Kurdistan’; and collective identity among secondgeneration German-Turks in the religions realm, involving Islamic thought and organizations, but also secular forms of everyday culture. The article concludes with a discussion of factors that may limit the future growth of transnational social spaces.