- The North American species of the shore fly genus Notiphila Fallen were taxonomically revised. Over 13,000 specimens were examined from throughout the Nearctic Region and information relating to the biology of many species occurring in the West was gathered from both field and laboratory studies. Previously used characters were reevaluated; new evidence from comparative morphological studies on the male and female postabdomens, from developmental stages, and from biological and ecological observations was collected. Forty-nine characters were selected, quantified, and analyzed using standard numerical taxonomic procedures. Collectively, all these data were assessed and a classification derived. Forty-seven Notiphila species are now recognized from North America. These have been further classified into two subgenera and six species-groups. The subgenera were first erected by E. T. Cresson, Jr. and have been substantiated by the additional evidence accumulated during this study. Likewise, the species-groups are essentially those of Cresson with additions and minor modifications. Recognition of the subgenus Notiphila is supported by the external morphology of both sexes, by the morphology of the pupae and larvae, and by phenetic analysis using quantitative procedures. This subgenus includes 25 North American species of which three species are resurrected from synonomy (N. bicolor Cresson, N. cognata Cresson, and N. unicolor), two new names are proposed N. cressoni and N. paludicola for N. bicolor and N. unicolor respectively), and 13 new species are described (N. adusta, N. footei, N. pallicornis, N. taenia, N. phaeopsis, N. pulcra, N. robusta, N. eleomyia, N. latigena, N. orienta, N. pauroura, N. poliosoma, and N. shewelli). These species have been arranged into three species-groups that are based primarily on characters of the male genitalia. Most of the species of this subgenus occur in eastern North America. The second subgenus, Agrolimna, comprises 22 species, including seven new species (N. scoliochaeta, N. atrata, N. deonieri, N. deserta, N. elophila, N. nanosoma, and N. paludia). In addition/ the following synonymies are proposed (older name first: N. decoris Williston = N. atrisetis Cresson, N. quadrisetosa Thomson = N. occidentalis Cresson, and N. pulchrifrons Loew = N. signata Cresson). N. transversa Walker, listed as an Agrolimna species in the latest North American catalog, is a species of the genus Dichaeta. Three species-groups are recognized for the North American species, and most species are distributed in western North America.