Diasporas, sometimes referred to as expatriates or transnational communities, play an important role in harnessing the benefits of migration for development. Measuring issues related to diaspora groups is difficult, as there is no common definition of "diasporas". Data on migrant stocks can serve as a proxy for diaspora populations, and remittance data are also closely related to the study of diasporas. Since the 1990s, many states have put in place extensive programmes to promote diaspora relations. However, differences in definitions and the lack of robust monitoring and evaluation make it difficult to compare these policies.  

Data on diaspora populations are difficult to collect, as emigrants are not automatically members of diasporas, and second- and third-generation descendants of migrants may also be considered or consider themselves to be part of a diaspora group. Generally, there is far more information available on diasporas than there are data.