ISSN 0707-5332 print/ISSN 1949-6540 online Ó 2011 Taylor & Francis http://dx. doi. org/10.1080/07075332.2011. 620735 http://www. tandfonline. com within customary, delineated spaces or containers, might they be states, nations, empire or regions. Consequently, all of these tools or perspectives stress the importance of the interaction and circulation of ideas, peoples, institutions or technologies across state or national boundaries and thus the entanglement and mutual influence of states, societies or cultures. According to such a definition transnational history is a perspective of study; it does not claim to be a specific method. 6 Among the well-established, yet expanding list of objects of transnational history, we may be confronted with a variety and to a certain extent some heterogeneity of topics: research on international institutions, NGOs, social movements, environment, imperial history, migration and diaspora or journeys and their impact on societies, groups or identities. 7 Transnational history may not be new. But the quantitative output of publications with ‘transnational’in the title has reached an unprecedented level over the past few years. If there have always been implicit transnational histories, the shift that is currently occurring is that it has become explicit over the past fifteen years or so. Whether transnational history has to be explicit or not is debatable, just as many national histories used to be rather implicit than explicit. 8 What has changed, then, is that transnational history is now explicit. But the interesting question is why now?