The Nearctic genus Neossos Malloch is revised. The genus contains three species: Neossos marylandicus Malloch (type locality: Bell, MD), Neossos californicus Melander (type locality: Corona del Mar, CA), and Neossos atlanticus n. sp. (type locality: Île Bonaventure, Quebec, Canada). All species are described and illustrated, and a key to species is provided. The male postabdomen of the genus is described in detail for the first time. All known specimens of Neossos have been collected from bird nests, and the larvae and adults are apparently closely associated with the nest material. Morphological differences between the three species of Neossos correspond to differences in avian hosts at the ordinal level, architecture of host nests, and geographic distribution. N. marylandicus is associated with cavity-nesting passerine birds in eastern North America, N. californicus with raptors in western North America, and N. atlanticus with colonial, cliff-nesting seabirds in eastern North America.