Dust storms are recognized as having a very wide range of environmental impacts. Their geomorphological interest lies in the amount of deflation and wind erosion they indicate and their role in loess formation. Atmospheric mineral-dust loading is one of the largest uncertainties in global climate-change modeling and is known to have an important impact on the radiation budget and atmospheric instability. Major gaps remain in our understanding of the geomorphological context of terrestrial sources and the transport mechanisms responsible for the production and distribution of atmospheric dust, all of which are important in reducing uncertainties in the modeling of past and future climate. Using meteorological data from ground stations, from the space-borne Total Ozone Monitoring Spectrometer (TOMS), and from the National Center for Environmental Prediction–National Center for Atmospheric Research reanalysis project, we illustrate the key source regions of dust and demonstrate the primacy of the Sahara. Objectively defined source regions for the Sahara are determined from eigenvector techniques applied to the TOMS data. Other key regions include the Middle East, Taklamakan, southwest Asia, central Australia, the Etosha and Mkgadikgadi basins of southern Africa, the Salar de Uyuni (Bolivia), and the Great Basin (United States). In most of these regions, large basins of internal drainage, as defined from a digital elevation model, are dust sources where the near-surface atmospheric circulation (determined by calculated means of potential sand flux) is favorable for dust mobilization. Surface observations indicate some regions as being important that do not appear on the TOMS maps. Possible reasons for these discrepancies are explored.