The North American representatives of the large, worldwide Geometrid moth genus Scopula Schrank are redefined, redescribed, and illustrated. Of 69 names applied to the North American fauna, 22 are considered valid species, and two subspecies are defined here for the first time. Complete synonymy and references are given. Over 5,400 specimens were borrowed for critical examination, and the types for all species were, if known to exist, examined by the author, or for him by a colleague. Redescriptions were made stressing the individual variability within each species. Features of male and female genitalia were used as well as external characters in assessing relationships. Lectotypes were designated when necessary. A neotype for Phalaena limboundata Haworth was created. A key to the males of North American Scopula is included, as well as drawings of male and female genitalia, photographs of the moths, and a check list to species, subspecies, and junior synonyms. The following nomenclatural changes were made: tawneata Cassino synonymized to aemulata Hulst; responsaria Walker, atomaria Warren, approbata Warren, trias Warren, and trias ab. tincta Warren synonymized to apparitaria Walker; canthema Schaus and hieronyma Prout synonymized to plantagenaria Hulst; umbilicata ab. cugia Schaus and umbilicata var. peruviana Prout synonymized to umbilicata Fabricius; quinqueliniaria Packard and johnstonaria McDunnough (justified emendation of johnsonaria) made subspecies ot junctaria Walker; impunctata Warren and vestalialis Barnes and McDunnough synonymized to junctaria quinquelinearia Packard; quadrilineata Packard resurrected from synonymy, and persimilis Hulst made a junior synonym of it once more; arcticaria Walker removed from synonymy of frigidaria Möschler, and placed in species incertae sedis; supressaria Walker removed from synonymy of inductata Guenée and placed in species incertae sedis; delicata Cassino and oliveata Cassino made junior synonyms of inductata Guenée; subfuscata Taylor placed in synonymy of luteolata Hulst; californiaria Packard and chretieni Barnes and Benjamin placed in synonymy of sideraria Guenée; nigrodiscalis Hulst and quaesitata Hulst placed in species incertae sedis. Apparitaria Walker is applied to the North American fauna for the first time. Siccata McDunnough and septentrionicola McDunnough are recorded for the first time from the United States. / Ph. D.