Species of the North American genus Platylygus Van Duzee 1915 are revised. Redescriptions are given for 5 previously known species, and 26 new species are described. Nineteen species described by Kelton are: angulatus, brevirostris, longirostris, and mexicanus from Durango, Mex.; aztecus from Mexico, Mex.; chamulans and chiapasensis from Chiapas, Mex.; alpinus from Chiapas, Mexico, and Puebla, Mex.; crassicornis from Mexico and Puebla, Mex.; pilosus and teocotae from Mexico, Mex.; pilosipes from Durango, Mex., and Arizona; scutellatus from Durango, Mex., Arizona, and New Mexico; contortae, crinitus, and magnus from California; knighti from Arizona and Colorado; piceicola from British Columbia, Yukon Territory, Arizona, and Colorado; pseudotsugae from British Columbia and Oregon. Seven species described by Knight are: keltoni from Durango, Mex.; andrei from Arizona; balli from Arizona, Colorado, and New Mexico; hirtus from Arizona; rolfsi from British Columbia, California, Oregon, and Washington; rubripes from Alberta, British Columbia, California, Colorado, Oregon, and Wyoming; and usingeri from California. The other species in the genus are: fuliginosus Knight from Arizona; grandis Knight from Arizona, California, and Colorado, Montana, and South Dakota; intermedius Knight from Arizona, Colorado and New Mexico; luridus (Reuter) from Alberta, British Columbia, Manitoba, New Brunswick, Nova Scotia, Ontario, Quebec, Saskatchewan, Yukon Territory, Arizona, Colorado, Illinois, New Hampshire, New Mexico, New York, and Wyoming; and vanduzeei Usinger from Arizona, California, Colorado, New Mexico, Nevada, and Utah. Platylygus uhleri (Van Duzee) is considered to be a synonym of P. luridus (Reuter). A key to species, records on distribution and biological data are included, and the male genitalia of all but one species are illustrated.