The descriptive taxonomic study reported here is focused onGlyptapanteles, a species-rich genus of hymenopteran parasitoid wasps. The species were found within the framework of two independent long-term Neotropical caterpillar rearing projects: northwestern Costa Rica (Área de Conservación Guanacaste, ACG) and eastern Andes, Ecuador (centered on Yanayacu Biological Station, YBS). One hundred thirty-six new species ofGlyptapantelesAshmead are described and all of them are authored by Arias-Penna. None of them was recorded in both countries; thus, 78 are from Costa Rica and the remaining 58 from Ecuador. Before this revision, the number of Neotropical describedGlyptapantelesdid not reach double digits. Reasonable boundaries among species were generated by integrating three datasets: Cytochrome Oxidase I (COI) gene sequencing data, natural history (host records), and external morphological characters. Each species description is accompanied by images and known geographical distribution. Characteristics such as shape, ornamentation, and location of spunGlyptapantelescocoons were imaged as well. Host-parasitoid associations and food plants are also here published for the first time. A total of 88 species within 84 genera in 15 Lepidoptera families was encountered as hosts in the field. With respect to food plants, these wild-caught parasitized caterpillars were reared on leaves of 147 species within 118 genera in 60 families. The majority ofGlyptapantelesspecies appeared to be relatively specialized on one family of Lepidoptera or even on some much lower level of taxonomic refinement. Those herbivores in turn are highly food-plant specialized, and once caterpillars were collected, early instars (1–3) yielded more parasitoids than later instars.Glyptapanteles jimmilleriArias-Penna,sp. nov.is the first egg-larval parasitoid recorded within the genus, though there may be many more since such natural history requires a more focused collection of eggs. The rate of hyperparasitoidism within the genus was approximately 4% and was represented byMesochorusspp. (Ichneumonidae). A single case of multiparasitoidism was reported,Copidosoma floridanumAshmead (Encyrtidae) andGlyptapanteles ilarisaaksjarviArias-Penna,sp. nov.both parasitoid species emerged from the caterpillar of Noctuidae:Condica cupienta(Cramer). Bodyguard behavior was observed in twoGlyptapantelesspecies:G. howelldalyiArias-Penna,sp. nov.andG. paulhansoniArias-Penna,sp. nov.A dichotomous key for all the new species is provided. The numerous species described here, and an equal number already reared but not formally described, signal a far greaterGlyptapantelesspecies richness in the Neotropics than suggested by the few described previously.