AbstractMorphological and distributional data are presented for North American species of the family Chappuisididae, including members of the genera Chappuisides Szalay (subfamily Chappuisidinae), Uchidastygacarus Imamura (subfamily Uchidastygacarinae), and Morimotacarus Imamura and Yachatsia Cook (subfamily Morimotacarinae). The phylogenetic relationships of mites in these subfamilies with other Arrenuroidea are discussed, leading to the conclusion that mites previously placed in the families Chappuisididae and Uchidastygacaridae Imamura probably represent a single, holophyletic group. As a result, the family Chappuisididae is redefined, and four subfamilies are recognized, namely Chappuisidinae, Uchidastygacarinae Imamura, Tsushimacarinae Cook, and Morimotacarinae Imamura. The name Uchidastygacaridae is placed in synonymy with Chappuisididae. New diagnoses are proposed for the family and subfamilies.Adults of Chappuisides eremitus Cook are redescribed, and adults of seven new species, namely C. anomalus sp.nov., C. neomexicanus sp.nov., C. acadianus sp.nov., C. cooki sp.nov., C. occidentalis sp.nov., C. californicus sp.nov., and C. oregonensis sp. nov., are described for the first time. Deutonymphs of C. acadianus, C. cooki, and C. occidentalis are also described. A new diagnosis is proposed for the genus Chappuisides and subgeneric concepts are reviewed critically.Adults of Uchidastygacarus (Imamurastygacarus) ovalis Cook, U. (s.s.) imamurai Cook, and U. (s.s.) acadiensis Smith are redescribed, largely on the basis of recently collected specimens including the first known adult males of U. (I.) ovalis. Adult males of U. (s.s.) magnificus sp.nov., adult females of U. virginiensis sp.nov., and deutonymphs and adults of both sexes of U. appalachianus sp.nov. are described for the first time. New diagnoses are proposed for the genus Uchidastygacarus and its subgenera.Adults of Morimotacarus nearcticus sp.nov., the first known nearctic species of the genus, are described and adults of Yachatsia mideopsoides Cook are redescribed. Deutonymphs of both of these species are described for the first time. The name Yachatsia euforma Habeeb is placed in synonymy with Y. mideopsoides based on study of type specimens and assessment of variability within populations. New diagnoses are proposed for the genera of Morimotacarinae.A phylogenetic framework for Chappuisididae is outlined and discussed. New distributional data are presented for North American species, permitting the first comprehensive attempt to assess the zoogeography of the family. The family probably differentiated from early derivative mideopsiform arrenuroid stock similar to Nudomideopsidae in Laurasia during the late Cretaceous or early Tertiary. Extant subfamilies apparently originated early in Tertiary times, and the clades that include modern genera dispersed throughout western North America and eastern Asia, and in some cases more extensively on both continents, between the early Tertiary and the Pleistocene. Climatic cooling in late Tertiary times, culminating in glacial episodes during the Pleistocene, resulted in displacement of chappuisidid taxa to various refugial areas south of continental ice sheets. Modern species are in the process of invading recently deglaciated areas in both eastern and western North America, but at differing rates that reflect their vagility, cold-tolerance, and ability to colonize newly established interstitial habitats. Chappuisididae have considerable potential value as indicators of the impact of environmental changes on interstitial freshwater ecosystems.