Genera and previously described species of Nearctic Scythrididae are revised for the first time, based on the study of adult structures. About 90 percent of the Nearctic fauna known in collections consists of undescribed species. The supraspecific taxa treated in this work encompass less than half of the Nearctic species diversity. Only six new species are described, all within the largest and structurally most diverse genus. The status of all nominal species is revised. Valid species are redescribed and their features illustrated. General problems in the systematics of the Scythrididae are discussed. A description of adult features of the family Scythrididae is providad. Extra-limital genera are briefly reviewed. A key to the Nearctic genera and informal supraspecific lineages is provided.Six genera, including three new, are treated: Areniscythris Powell, 1976, Arotrura Walsingham, 1888, Asymmetrura gen. nov., Neoscythris gen. nov., Rhamphura gen. nov., and Scythris s. str. Hübner, . Areniscythris includes a single described species, Areniscythris brachypteris Powell, but is defined more broadly to account for a number of undescribed species. Arotrura is divided into nine informal species groups with the following included species: Arotrura atascosa sp. nov., Arotrura balli sp. nov., Arotrura divaricata (Braun) comb, nov., Arotrura eburnea Walsingham, Arotrura formidabilis sp. nov., Arotrura hymenata sp. nov., Arotrura longissima sp. nov., Arotrura oxyplecta (Meyrick) comb, nov., Arotrura powelli sp. nov., and Arotrura sponsella (Busck) comb. nov. Asymmetrura includes: Asymmetrura albilineata (Walsingham) comb. nov., Asymmetrura graminivorella (Braun) comb. nov., Asymmetrura impositella (Zeller) comb. nov. and type species, Asymmetrura matutella (Clemens) comb, nov., Asymmetrura reducta (Braun) comb, nov., and Asymmetrura scintillifera (Braun) comb. nov. Neoscythris includes: Neoscythris confinis (Braun) comb, nov., Neoscythris euthia (Walsingham) comb. nov., Neoscythris fissirostris (Meyrick) comb. nov. and type species, and Neoscythris planipenella (Chambers) comb. nov. Rhamphura includes: Rhamphura altisierrae (Keifer) comb, nov., Rhamphura ochristriata (Walsingham) comb. nov. and type species, Rhamphura perspicillella (Walsingham) comb. nov., Rhamphura suffusa (Walsingham) comb. nov., and the extra-limital Rhamphura immunis (Meyrick) comb. nov. from Peru. Scythris s. str. includes: Scythris immaculatella (Chambers) rev. stat., Scythris limbella (Fabricius), Scythris mixaula Meyrick, Scythris trivinctella (Zeller), and Scythris ypsilon Braun. A further eight species are phylogenetically distinct from Scythris s. str. but provisionally are only assigned to five informal monophyletic lineages until their cladistic relationships are more firmly established. These are: the Scythris basilaris lineage including Scythris basilaris (Zeller), Scythris eboracensis (Zeller), and Scythris fuscicomella (Clemens); the Scythris interrupta lineage including Scythris interrupta Braun; the Scythris inspersella lineage including Scythris inspersella (Hübner) and Scythris noricella (Zeller); the Scythris anthracina lineage including Scythris anthracina Braun; and the Scythris charon lineage including Scythris charon Meyrick. Three species are incertae sedis: Scythris inornatella (Chambers) comb, nov., Scythrispilosella (Zeller), and Scythris piratica Meyrick.Coleophora albacostella Chambers and Coleophora inornatella Chambers are transferred from the Coleophoridae. Scythris arizoniella (Kearfott) is transferred to the Coleophoridae [Coleophora arizoniella (Kearfott) comb. nov.].The following new synonymy is proposed: Colinita Busck, 1907 = Arotrura Walsingham, 1888; Gelechia aterrimella Walker, 1864 and Scythris epilobiella McDunnough, 1942 = Scythris inspersella [Hübner, (1817)]; Scythris magnatella Busck, 1904 = Scythris noricella (Zeller, 1843); Scythris pacifica McDunnough, 1927 = Scythris immaculatella (Chambers, 1875); Coleophora albacostella Chambers, 1875 and Scythris hemidictyas Meyrick, 1928 = Neoscythris planipenella (Chambers, 1875).A cladistic definition of the family is presented for the first time. The monophyly of the Scythrididae is supported by the following synapomorphies: very narrow ductus bursae, broad ductus seminalis anastomosed with the oviduct and the corpus bursae, lack of signum, unique shape of the apophyses of the metathoracic furca, tarsomeres 1–4 with two subapical spurs, aedeagus ankylosed, and origin of forewing veins R4 and R5 on a common stalk with R4 extended to the costa and R5 to the termen. Relationships of the Scythrididae within the Gelechioidea are discussed. Based on the cladistic analysis of 52 structural characters, phylogenetic relationships of supraspecific taxa are inferred. Two cladograms, one for the genera and one for the species groups of Arotrura, are presented and used in deriving the classification.