Euphorbia L. (Euphorbiaceae), one of the largest genera of angiosperms, is represented in the Caucasus by 80 species. This paper contains a taxonomic treatment for these species and a key for their determination. For every species the following information is provided: accepted name and major synonyms with typification where possible; brief characteristics of habitats; distribution in the Caucasus and indication of geographical element (for indigenous species); and taxonomic and geographical notes if necessary. Lectotypes of Euphorbia arvalis Boiss. et Heldr., E. damascena Boiss., E. fossulata Boiss. et Gaill., E. iberica Boiss. var. intermedia Boiss., E. kemulariae Ter-Chatsch., E. notadenia Boiss. et Hohen., E. platyphyllos L., E. paralias L. and E. ruderalis Sheele are newly designated. The indigenous component of Caucasian Euphorbia comprises 73 species. The majority belong to three geographical elements: Euro-Siberian (41.10%), Irano-Turanian (20.54%) and Submediterranean (15.07%). There are also 7 alien species mostly of North American origin. Taxonomically, most of Caucasian Euphorbia species (70 or 87.5%) belong to subgen. Esula and represent 16 of the 21 currently accepted sections. The remaining ten species belong to subgen. Chamaesyce.