A new study of specimens of paromomyid and microsyopid primates clarifies evolution in these primates and results in new concepts of each family. The paromomyid Phenacolemur and its former synonym, Ignacius, are distinct genera, each with new Early Wasatchian species. Plesiolestes, Palaechthon, Torrejonia, Palenochtha, Navajovius, Micromomys, and Tinimomys are removed from the Paromomyidae and transferred to the Microsyopidae. The Plesiadapiformes are classified in three groups which may be differentiated on incisor and molar structure: Plesiadapoidea (Plesiadapidae, Carpolestidae, and Saxonel-lidae), Microsyopidae, and Paromomyidae. The Paromomyidae, Microsyopidae (and its two subfamilies), and several genera are rediagnosed in the light of new comparative evidence.