The large and complex genus Euxoa is divided into six subgenera: Orosagrotis, Longivesica, Euxoa, Chorizagrotis, Pleonectopoda, and Crassivesica. Orosagrotis and Chorizagrotis have until now been considered as valid noctuid genera by many workers. Longivesica and Crassivesica are here described as new. The taxonomy and distribution of North American species in all subgenera except the very extensive subgenus Euxoa are considered in the present paper. Only 49 species in a probable North American Euxoa fauna of some 200 species are included in the five subgenera reviewed here, however.Within the genus, species have been segregated into subgenera and species groups largely on the basis of the structure of the male genitalia, and particularly on the conformation of the vesica of the male. Keys to subgenera, species groups, and species are presented. No new species are described. Subspecies are not formally considered because an adequate analysis of the often complex geographic variation is beyond the scope of this paper.