Platygastroid wasps preserved in Dominican amber and oil shale from the Kishenehn formation (Montana, USA) in the National Museum of Natural History are catalogued. Compression fossils in Kishenehn oil shale yield a specimen of Fidiobia, a specimen of Telenominae, and a specimen with a Scelio-type ovipositor system. Twenty-five described genera are documented from Dominican amber, all of which are known from the extant fauna: Allostemma Masner & Huggert, Aradophagus Ashmead, Calliscelio Ashmead, Calotelea Westwood, Duta Nixon, Embidobia Ashmead, Embioctonus Masner, Fidiobia Ashmead, Gryon Haliday, Idris Förster, Inostemma Haliday, Leptacis Förster, Leptoteleia Kieffer, Macroteleia Kieffer, Odontacolus Kieffer, Opisthacantha Ashmead, Parabaeus Kieffer, Paridris Kieffer, Platygaster Latreille, Plaumannion Masner & Johnson, Probaryconus Kieffer, Psilanteris Kieffer, Spiniteleia Masner, Telenomus Haliday, and Triteleia Kieffer. Fourteen of these genera do not have previously published fossil records and are here documented for the first time. Plaumannion fistulosum Talamas, sp. n., and Paridris yumai Talamas, sp. n. are described as new species. A phylogenetic analysis of Paridris including P. yumai is presented. A male specimen belonging to an undescribed scelionine genus is documented and illustrated, but not described, as the best features for circumscribing this taxon are found in the female, and monographic work on this group is currently underway by other workers. Four specimens from Baltic amber, belonging to Leptacis, Platygaster, and Sembilanocera Brues are presented for comparison to extant specimens and inclusions in Dominican amber.
