This study explores the impact of the brain drain on a source country’s welfare and development, which can either be beneficial or harmful. The evidence suggests that there are many more losers than winners among developing countries. Whether a country gains or loses depends on country-specific factors, such as the level and composition of migration, the country’s level of development, and such characteristics as population size, language, and geographic location. It recommends that policymakers gauge the costs and benefits of the brain drain in order to design appropriate policy responses.