This chapter discusses trans-border ethnic populations in the former Soviet Union in a broader conceptual context, highlighting the importance of diaspora issues both for post-Sovietologists and for scholars of comparative politics and international relations in general. It explains the use of the label "diaspora" even for ethnic communities that have arrived "abroad" only because of sudden changes in international frontiers. In 1991 a scholarly journal was established with the aim of promoting the study of diaspora issues in what the editor, in the inaugural issue, described as the world's new "transnational moment". The return of diasporic populations to their homelands has been especially evident in postcommunist Europe. Ethnic diasporas can clearly influence state policy, whether within the states in which they live or within their putative ethnic homelands. The post-Soviet case demonstrates the potential uses of ethnicity as a political instrument in both domestic politics and foreign policy.