The moth subfamily Dioptinae is almost entirely neotropical. One species—Phryganidia californica—occurs on the west coast of the US, while the remaining taxa are found from Mexico south to northern Argentina and Uruguay. None is known from the Old World. Most dioptines are diurnal as adults, and many exhibit aposematic coloration. A few taxa are nocturnal. Their larval hosts include the families Passifloraceae, Violaceae and Poaceae, plants famous for their use by important butterfly groups.

In this paper, a revised generic classification for the Dioptinae is presented. Nearly 17,000 specimens, assembled from 38 private and institutional collections worldwide, form the basis for the first comprehensive analysis of adult morphology in the subfamily. A subset of 115 exemplar species, chosen to represent structural diversity across the Dioptinae, is subjected to detailed morphological study and cladistic analysis. The resulting matrix includes 305 characters delineated by 938 character states. Cladistic analyses produced a single most parsimonious tree, rooted using three species from the Nystaleinae—the sister-subfamily to the Dioptinae. This phylogenetic hypothesis provides the framework for a revised classification.

The 456 species are assigned to 43 genera in two tribes; 10 species are treated as incertae sedis. Twelve genera are synonymized, and seven—Argentala, Chrysoglossa, Nebulosa, Notascea, Pikroprion, Proutiella, and Sagittala—are described as new. The 36 remaining genera are redescribed. Sixteen genera are further subdivided into species groups. All 574 species-group names of previous authors are addressed; in nearly all cases, primary type material was examined. Forty-seven species are newly synonymized, while 31 names are revived from synonymy. The revised classification includes 118 new combinations. Sixty-four species belonging in 30 different genera are newly described from Brazil, Colombia, Costa Rica, Ecuador, French Guiana, Guyana, Mexico, Panama, Peru, and Venezuela.

An illustrated overview of dioptine morphology is presented, demonstrating remarkable variation in a wide range of structures. Dichotomous keys utilizing external adult anatomy are provided to the tribes, genera, species groups and species. The salient features of each genus are figured and described. Heads, labial palpi, antennae, metathoracic tympani, wing scales, wing venation, and male and female terminalia are shown through line drawings, photographs, and scanning electron micrographs. Each species is diagnosed, its habitus is illustrated in color, type material is notated, and a summary of its known geographical distribution is presented.

General themes, as exemplified by the Dioptinae, are discussed. These include: Estimating species diversity in neotropical Lepidoptera; the evolution of aposematic coloration and mimicry; patterns of host-plant use; and the potential utility of characters from immature stages and DNA for further refining our understanding of dioptine evolution.