This is monograph 110 in the Flora Neotropica series. This monograph is the culmination of more than 40 years of field and laboratory studies of a large and morphologically complex genus. With about 150 species Jatropha constitutes a taxon of diverse woody group in the Euphorbiaceae and is considered to be the most primitive member of the family. It has a disjunct geographical distribution, with nearly two-thirds of the known species in the Americas and most of the remainder in tropical Africa, and a few species in Arabia and India. Diversity of the genus is best reflected in the radically different classifications of the past as well as those of modern taxonomists. All but one of the 10 generic names has been applied to the neotropical species. With notable addition of new sections and subsections previous infrageneric treatment of the genus by Dehgan and Webster (1979) has been to a large extent revised. Taxonomic history with addition of some new information is presented as well as a discussion of lectotypification of the genus. Results of previously published studies of morphological, anatomical, phenetic, and phylogenetic analyses as well as some recent work are used as the bases of classifications. The monograph is a fully illustrated comprehensive treatment of the neotropical taxa, including their geographical distribution, medicinal and other uses, as well as other relevant information.