Tenebrionidae is represented from all major biogeographical regions of the world and from widely varied habitats. At present, there are approximately 20,000 species described worldwide in more than 2,300 genera. The family is the largest in Tenebrionoidea, and is currently the fifth largest in Coleoptera. Most of the approximately 200 genera and well over 1,000 species in the United States inhabit arid regions of the Mountain and Western states. Approximately 250 species are recognized east of the Mississippi River, with undoubtedly more to be discovered and described. The scope of the species discussed here is based primarily on political boundaries but should serve as a good indication of which species have ranges skewed either to the north, south, east or west on a more biologically natural scale. Many species have distributions that extend west beyond the Mississippi River, north into Canada and south into the Caribbean, Mexico, Central and South America. While the bulk of North American tenebrionid diversity remains in the arid west, many derived tenebrionid groups are represented in the mesic forests of eastern North America and comprise a significant part of our regional entomofauna.