A revision of the genus Asteromyia Felt is presented, and 7 species are recognized: A. carbonifera (Osten Sacken), A. clarkei (Felt), n. comb., A. laeviana (Felt), A. modesta (Felt), A. chrysothamni Felt, A. cuthamiae, n. sp., and A. gutierreziae Felt. There are 23 new synonyms. The genus is exclusively New World in distribution, and its species cause galls in the leaves and green stems of plants in the tribe Astereae (Compositae). The morphology of A. carbonifera is presented with illustrations. Descriptions of the galls, larvae, pupae, and adults of the 7 species are given, as well as keys to the larvae and adults. Also, systematic relationships and the biology of Asteromyia are discussed, as arc the generic relationships of the host plants. Five species formerly placed in Asteromyia are transferred elsewhere: Neolasioptera canadensis (Felt), n. comb.; N. petiolicola (Felt), n. comb, and n. syn. of N. vitinea (Felt); N. phragmites (Felt), n. comb.; N. agrostis (Osten Sacken), n. comb.; and urostigmatis Tavares as an unplaced species of Cecidomyiidae. The name Neolasioptera agrostis Felt, a junior homonym, consequently is changed to the available name N. agrostidis Kieffer.