The classification of the Nearctic species of the subgenus Orthocladius (Orthocladius) van der Wulp is revised; keys to species for males, females, pupae, and larvae are given; 65 characters in the adult male are taxonomically evaluated; and keys to and diagnoses of the species of the subgenera of Orthocladius for males, females, pupae, and larvae are given. Twenty-nine names of O. (Orthocladius) are recognized as valid. Redescriptions of 17 previously-known species and descriptions of 11 new species are presented. The new species are: O. appersoni, O. charensis, O. clarkei, O. cooki, O. hazenensis, O. hellenthali, O. knuthi, O. oliveri, O. robacki, O. subletti, and O. tryoni. Orthocladius paradorenus (Roback) is considered as a synonym of O. obumbratus Johannsen, and O. currani Sublette is considered as a synonym of O. dorenus (Roback); O. nanseni Kieffer and O. sordens Johannsen are considered as nomina dubia; O. bifasciatus Malloch and O. clepsydrus Coquillett are incertae sedis. Lectotypes are designated for Chironomus decoratus Holmgren, O. dentifer Brundin, O. excavatus Brundin, O. lapponicus Goetghebuer, O. obumbratus Johannsen, and O. trigonolabis Edwards. Orthocladius dentifer Brundin, O. excavatus Brundin, and O. smolandicus Brundin are new records from North America. Orthocladius glacialis Kieffer probably does not occur in North America. Orthocladius oblidens (Walker) is accepted as the type-species of the genus Orthocladius.