Technical Abstract: The genus Lotus consists of 172 species; a list of the species is presented. Of this total, 48 species are known only from the New World, and 124 from the Old World. It is most species rich in regions with Mediterranean climate, i.e., the Mediterranean basin and the far western United States and northwestern Mexico. It occurs throughout the continents sof Africa, Europe, Asia, Australia, and North America, is abundant in Macaronesia, and is represented in both northern Central America and Chile by single species. Lotus species recognized in the Old World are more narrowly defined than those recognized in the New World. The large number of species in the Old World is partially attributable to this. Most twentieth century Old World Lotus taxonomists have defined Lotus species narrowly, with some notable exceptions, and can, in general, be referred to as "splitters." Twentieth century New World Lotus taxonomists have delimited species more broadly, and, in general, can be referred to as "lumpers." The most economically important species are described, and a key is given for their identification.