Research on migration and development has recently changed, in two ways. First, it has grown sharply in volume, emerging as a proper subfield. Second, while it once embraced principally rural-urban migration and international remittances, migration and development research has broadened to consider a range of international development processes. These include human capital investment, global diaspora networks, circular or temporary migration, and the transfer of technology and cultural norms. To introduce a special issue of World Development on migration and development, we present a selection of frontier migrant-and-development research that instantiates these trends.