This chapter examines transnationalism in migration studies. First, we investigate the initial conceptualizations of the transnational perspective on migration and efforts at systematization. Second, we evaluate the discussions around contentious issues regarding past vs. present transnationalism, the extent of transnationalism among migrants, and transnationalism, globalization, states and politics. We outline a typology of transnationalism in which transnational social spaces are differentiated according to the internal characteristics of group organization and the extent of common or shared values and symbols. Third, we examine methodological notes on transnational research where we assess the term transnationality. We identify multiple research techniques used in transnational studies and conclude that nowadays mixed methods research is on the rise. Finally, we offer some venues for further research through a transnational optic where the focus should be on changing boundaries as social spaces are composed of dynamic processes.