The transnational approach in migration studies emerged in the early 1990s at a time when a greater attention was paid to non-state actors in the international realm. If both transnationalism and the concept of diaspora display distinct genealogies (the first concept coming from international relations, the second having a much older background), both are related. It is not a coincidence that Diaspora, a leading journal in this domain in 1991, is subtitled ‘a journal of transnational studies’. Admittedly, diasporas are regarded as a specific form of transnational community; the former concept insisting on identity formation and mobilization, the latter on ties and practices (Faist 2010: 11). And yet, the theoretical link between the two realities remains unclear. How do we shift from a transnational social field to a diaspora group? What is the bearing of collective memory and trauma (two key defining criteria characterizing diasporas) on cross-border ties and practices? This link is all the more complex to unfold as the concept of diaspora is itself evolving and polysemic. There is no widely shared definition of what a diaspora is, even more so since the term has fallen outside of the realm of scholarly debates and has been adopted by policy-makers.