There is now a third generation of transnational scholarship, which goes beyond the analysis of cross-border ties and looks at the genesis, reproduction and change of boundaries in social spaces, both within and across nation-state borders. This analysis proceeds in five steps. The first describes three generations and directions of transnational scholarship. The second part introduces the more specific concepts of transnationalization and transnationality. At the centre of the third part is a comparison of transnational and global and world approaches. A transnational lens looks at how boundaries in cross-border settings evolve and change. The fourth part focuses on the concepts of boundary and social space. The perspective is process-oriented and shows how borders and boundaries are redrawn in a period of intense restructuration of capital, changing geopolitical constellations and new constellations of cultural diversity. In order to move towards causal analysis of boundary change, the fifth part uses a case study to consider the social mechanisms operative in the (un)making of boundaries along diverse characteristics, such as religion, class, ethnicity, and gender. The question for future research is to integrate various (spatial) scales of analysis to arrive at a better understanding of changing forms of social inequality across borders.