The vast rangelands of south Texas--that portion of the state lying south of San Antonio and extending west and south to the Rio Grande and east to the Gulf of Mexico--are home to many species of grasses, some beneficial and some noxious. Careful identification is important for ranch and farm management, conservation, and scientific study. This field guide catalogs 250 taxa, representing 9 subfamilies, 15 tribes, and 88 genera. Detailed descriptions, accompanied by color photographs, cover 175 native species and 75 that were introduced--exotic invaders that took hold as agricultural practices, urban development, road construction, and other perturbations eliminated extensive areas of native vegetation. High-resolution photographic scans of pressed field samples show detailed characteristics necessary for identification. Included for each species are common and scientific names and their importance to livestock, wildlife, and man. Detailed keys are provided for the genera and species covered. Although the guide covers grasses that occur in a 31-county area, the extensive ranges of many represented species also make Grasses of South Texas a useful reference for other areas of the state, the American Southwest and the Great Plains, and northern Mexico.