Introduction Over the last few years, the concepts and categories of transnational migration studies (Faist, Fauser, & Reisenauer, 2013; Levitt & Jaworsky, 2007) – already well-established across other disciplines – have successfully entered into the educational, theoretical, and practical field of social work. In this article we briefly take stock of this new development, in order to build a framework for the papers that follow. The contributions in this Mapping Transnationalism Section are authored by European leading scholars, with distinct and complementary takes on the emergence of a transnational turn in social work. In the first article, Karen Lyons advances a theoretical approach to social work with mobile populations, based on a conceptual revisit of international social work; in the second paper, in an educationally-oriented perspective, Pat Cox makes a case for a transnational optic to be more systematically assumed in academic curricula; in the last article, Norma Montesino and Mercedes Jiménez-Álvarez discuss the prospects for social work practice with a client group with a strongly transnational profile, such as so-called “unaccompanied minors.”1 What is specific to our own introductory piece, instead, is a three-step argument: a discussion of the conceptual grounds and the external factors underlying the transition from international to transnational social work (Section 1); an overview of the practical forms of transnational social work in the context of migration and of the types of resources circulated through them (Section 2); a preliminary balance of the professional implications of transnational social work with migrants, and of the challenges ahead for its refinement and diffusion (Section 3).