One person’s weed is another’s wildflower, but in this book weeds of southern Texas and northern Mexico are defined as plants that are considered a nuisance to farmers or noxious to livestock in the region. The book covers 189 broad-leaved herbaceous species, grasslike plants, and grasses, encompassing 144 genera and 45 families. These include one species of fern, 142 species of dicots, and 46 species of monocots. Of the dicots, 111 species of dicots are native and 31 are introduced. Twenty-one species of monocots are native, and 25 are introduced. The species descriptions include color photographs, family names, common names, scientific names, general descriptions, and the ecological characteristics of the weeds. Voucher specimens for most of the plants are on file in the University of Texas - Pan American Herbarium. Although this book focuses on plants that occur on both sides of the Rio Grande in Texas and northern Mexico, the extensive ranges of many of the represented species make it a useful reference for weeds in other areas of Texas and the southwestern United States. This book will be useful to farmers and farm managers, agricultural consultants, ranchers, natural resource managers, scientists, and anyone interested in the flora of southern Texas and northern Mexico.