Solanum section Geminata s.l. includes about 126 species of shrubs and small trees native to the Neotropics. Members of this section range from northern Mexico and the West Indies throughout South America to Uruguay and northern Argentina. A single species is native to the paleotropics, ranging from China to tropical Australia, and is also unusual in the group in that it is polyploid. Some species traditionally included in Pseudocapsicum, Indubitaria, and Holophylla, which have tended to be artificial groupings of apparently unrelated taxa, are included in this monograph. The monograph treats the taxonomic history, morphology, ecology (including extensive data on pollination and herbivory), and natural history of Solanum section Geminata.