We have examined 893 preserved frogs, including the type specimens of all included nominal taxa, 8 skeletons, 1 lot of eggs, and 3 lots of tadpoles that we refer to the genus _Osteocephalus_; in addition skulls were removed from five preserved specimens, and radiographs were made of 12 other preserved specimens. We have been fortunate in seeing living individuals of all species, except _O. pearsoni_, but we have colored photographs of a living specimen of that species. Figures 1 and 2 were drawn from projected colored transparencies of living frogs. Terminology follows that of Duellman (1970b). On the distribution maps solid symbols indicate localities from which we have examined specimens; open symbols represent additional locality records based on the literature. Throughout the text specimens are listed by their catalogue numbers preceded by the appropriate museum abbreviation, as follows: AMNH American Museum of Natural History ANSP Academy of Natural Sciences of Philadelphia ASU Arizona State University AUM Auburn University Museum BMNH British Museum (Natural History) CAS California Academy of Sciences CAS-SU Stanford University Collection (In California Academy of Sciences) CM Carnegie Museum FMNH Field Museum of Natural History KU University of Kansas Museum of Natural History MCZ Museum of Comparative Zoology, Harvard University MIZS Museo ed Istituto di Zoologi Sistematico, Universita di Torino MJP Museo Javier Prado, Lima MNHN Museum National d'Histoire Naturelle, Paris MPEG Museu Paraense Emiliano Goeldi, Belem MVZ Museum of Vertebrate Zoology, University of California, Berkeley MZUSP Museu de Zoologia, Universidade da Sao Paulo NHMG Naturhistoriska Museet Goeteborg NHMW Naturhistorisches Museum, Wien NHRM Naturhistoriska Riksmuseet, Stockholm RMNH Rijksmuseum van Natuurlijke Histoire, Leiden SMF Senckenbergische Museum, Frankfurt UIMNH University of Illinois, Museum of Natural History UMMZ University of Michigan Museum of Zoology UP Universite de Paris UPR-M University of Puerto Rico, Mayagueez UTA University of Texas, Arlington USNM United States National Museum UZM Universitets Zoologiske Museum, Copenhagen WCAB Werner C. A. Bokermann, Sao Paulo, Brasil ZMB Zoologisches Museum Berlin ZSM Zoologisches Sammlung Muenchen HISTORICAL RESUME Because of the taxonomic confusion that has surrounded the generic name _Osteocephalus_ and two of the species (and their synonyms), we present a brief resume of the taxonomic history of the group.