The late-instar larvae of about 185 species of the North American Olethreutidae are described and most of them illustrated. Included in these are many pests, such as Grapholitha molesta, Carpocapsa pomonella, and Spilonota ocellana on fruit trees, Paralobesia viteana on grapes, Ancylis comptana fragariae on strawberries, Laspeyresia nigricana in pea pods, Laspeyresia caryana in hickory and pecan nuts, Taniva albolineana in spruce needles, and species of Rhyacionia and Petrova on pines. Keys to species groups and to individual species are provided. Of the diagnostic and specialized characters listed, the most useful include the setae, the spinneret, and the shape of the larva, especially of its head and anal shield. The main characters are given for the postulated ancestral larva and for the highly developed larva. Most of the species groups are arranged according to the suggested phylogenetic relationship of their larvae, emphasizing the necessity of a revision of the family. Larvae of some genera previously difficult to classify, such as Pseudogalleria and Hystricophora, indicate the relationship of those genera to other groups; conversely, lack of relationship is clearly shown in other instances, e.g., between Carpocapsa pomonella and Carpocapsa saltitans, and between the two species Epiblema culminana and E. suffusana and other members of the genus Epiblema.