Political transnationalism covers a wide range of phenomena and can be studied using a variety of approaches. In migration research the focus is mostly on migrants' networks and activities that involve them in politics oriented towards their country of origin. The article argues for a wider conception of political transnationalism from a political theory perspective. It proposes a terminological distinction between international, multinational, supranational and transnational relations and phenomena. What is specific about migrant transnationalism is that it creates overlapping memberships between territorially separated and independent polities. In this understanding, political transnationalism is not only about a narrowly conceived set of activities through which migrants become involved in the domestic politics of their home countries; it also affects collective identities and conceptions of citizenship among the native populations in both receiving and sending societies. Within this general framework the article suggests a set of hypotheses for an explanatory and normative analysis of sending country relations to their emigrants, a task that has hitherto been neglected in political theory.