—The mineralogy of loess and loess-like sediments has important implications for the mechanisms of postdepositional alteration, as well as for environmental and geotechnical issues. The geotechnical properties of soils, their mechanical strength, and the bearing capacity of the soil foundations depend on the mineral species, their percentages, and relationships. Clay minerals control the mass transport processes which have bearing on pollution of ground and waters. Loess covers vast territories in all continents, including southern Russia, West Siberia, southern East Siberia, Russian Far East, Transbaikalia, and other regions. Loess and loess-like sediments have specific genetic, lithological, geotechnical, stratigraphic, and geomorphic features. The mineralogy of Quaternary loess has been studied using X-ray diffraction, chemical, and particle size analyses, following the standard techniques, with reference to earlier published evidence. The study area comprises three watershed provinces in the southeastern Russian Plain (southern European Russia). The results have geotechnical and environmental applications for loess provinces.