AbstractThe oribatid family Eremaeidae is represented in North America by two genera,EremaeusandEueremaeus, both widely distributed throughout the Palaearctic and Nearctic regions. In North America species in both genera are found in moist to arid habitats from New Mexico to the High Arctic. Reproduction is sexual, and both immatures and adults feed mainly on fungi.Revised diagnoses are presented for the Eremaeidae and generaEremaeusandEueremaeus. Eighteen species ofEremaeus, of which 14 are newly proposed, and 24 species ofEueremaeus, of which 15 are newly proposed, are recognized. Identification keys are provided for the world genera of Eremaeidae, and for adults ofEremaeusandEueremaeusof North America. All but one North American species of these genera are described, and their geographical distributions mapped.North AmericanEremaeusspecies includeE.appalachicussp. no v.,E.boreomontanussp. nov.,E.brevitarsus(Ewing),E.californiensissp. nov.,E.gracilissp. nov.,E.grandisHammer,E.kananaskissp. nov.,E.kevanisp. nov.,E.megistossp. nov.,E.monticolussp. nov.,E.nortonisp. nov.,E.occidentalissp. nov.,E.oresbiossp. nov.,E.plumosusWoolley,E.porosussp. nov.,E.salishsp. nov.,E.translamellatusHammer, andE.walterisp. nov. The immatures of four of these,E.kananaskis,E.occidentalis,E.oresbios, andE.translamellatus, are described.North AmericanEueremaeusincludeEu.acostulatussp. nov.,Eu.aridulussp. nov.,Eu.columbianus(Berlese),Eu.foveolatus(Hammer),Eu.marshallisp. nov.,Eu.masinasinsp. nov.,Eu.michaelisp. nov.,Eu.nahanisp. nov.,Eu.nemoralissp. nov.,Eu.proximus(Berlese) comb, nov.,Eu.woolleyi(Higgins) comb, nov.,Eu.yukonensissp. nov., and three informal species groups with the following included species in North America: (1)Eu.trionusgroup—Eu.trionus(Higgins) comb, nov., (2)Eu.stiktosgroup—Eu.carinatussp. nov.,Eu.higginsisp. nov.,Eu.stiktos(Higgins) comb, nov.,Eu.tetrosus(Higgins) comb, nov., (3)Eu.chiatousgroup—Eu.alvordensissp. nov.,Eu.aysineepsp. nov.,Eu.chiatous(Higgins) comb, nov.,Eu.danossp. nov.,Eu.lindquistisp. nov.,Eu.magniporosus(Wallwork) comb, nov., andEu.osoyoosensissp. nov. The immatures of nine of these,Eu.masinasin,Eu.nahani,Eu.carinatus,Eu.higginsi,Eu.columbianus,Eu.proximus,Eu.woolleyi,Eu.stiktos, andEu.tetrosus, are described.Kartoeremaeus reevesiHiggins andEremaeus politusBanks are considered junior subjective synonyms ofEueremaeus columbianus(Berlese).A cladistic analysis of the genera comprising Eremaeidae:Eremaeus,Tricheremaeus,Eueremaeus(and included species groups),Proteremaeus,Carinabella, andAsperemaeus, indicates thatEremaeusis the sister taxon ofCarinabella, and thatEueremaeusis the sister taxon ofProteremaeus.Tricheremaeusis the sister taxon ofEremaeus+Carinabella, andAsperemaeusis the sister taxon ofEueremaeus+Proteremaeus. The relationship of the Eremaeidae to the Megeremaeidae and Zetorchestidae is presented. Finally, I discuss the ecology and distribution of North American species of Eremaeidae.