ABSTRACT The increase in international migration to rich countries during the last two decades has spurred research and policy questions. The economic determinants of national and international migrations and the impact of immigrants on labor markets have been investigated by economists, geographers, and regional scientists for a long time. Recently, however, the availability of new and detailed individual data on migrants across regions and localities in several countries has made it possible to analyze the impact of immigration on a richer set of socio-economic outcomes. Two avenues of research have emerged as particularly interesting and are the focus of this special issue. First, international migrants are particularly concentrated in urban areas but their impact on some outcomes that are particularly relevant in cities (such as crime and housing markets) are not well understood yet. Second, immigrants not only increase labor supply but also affect firms’ productivity, survival and growth through their impact on localized externalities. These two themes link all the contributions of this special issue and show new directions for future research on the impact of immigration.