This is the first of three CREST-funded Thematic Reports published by a team of researchers at City, University of London, and Cranfield University at the Defence Academy of the United Kingdom examining political action among diaspora populations. The purpose of the report is to explore the theoretical and conceptual basis underpinning academic debates on engagement in the politics of conflict and post-conflict by communities living overseas. The research team is interested specifically in the Sri Lankan civil conflict between 1983 and 2009 and its aftermath, and understanding the attitudes towards and involvement in that conflict on the part of Tamil diaspora communities. The CREST project is exploring diaspora communities’ relationship with the changing socio-political environment in the homeland and how this influences processes of radicalisation or moderation. It recognises that the socio-political circumstances in which these processes develop are often crucial when understanding why a community or individuals within that community abroad act in a certain way; this includes analysis of different scales and levels of engagement, both in home countries and in host countries, as well as different ‘areas’ of engagement, which can range from social to economic to political interactions. The following review is not specific to the Sri Lankan situation; it is rather concerned with how four concepts, diaspora, transnationalism, cosmopolitanism, and translocalism, have come to frame the academic discussion on diaspora, or more broadly overseas politics and the potential of the concepts to shed light on the relationship between mobility and political action. It considers the extent to which these concepts are helpful in identifying the rationale behind specific methods of political participation, offering critical reflections on the analytical and normative usefulness of these terms.ESRC Award: ES/N009614/1