This paper reviews available data sources for the study of migration and development through both retrospective and continuous data collection systems. It is argued that much basic data already exists for the study of international migration but that the addition of a relatively small number of simple, although not necessarily cheap measures can be taken to improve existing data. The priority is to generate flow data between countries for recent time periods and the paper makes suggestions how this can be best achieved. The paper goes on to an assessment of the types and availability of data needed to understand better the relationships between migration and development more broadly. Data at several scales, macro and micro, and for a variety of types of migration will be required in order to achieve this objective, particularly if less visible flows, such as those internal to developing countries, or those involving women, are to be better understood. The paper concludes by moving beyond the traditional state-led data-gathering systems to examine the potential for civil society organizations to help in strengthening data and research on migration and development.