The fern flora of Mexico is poorly known. Serious, sustained collecting of ferns and close study of herbarium specimens have resulted in a great amount of new material, not only of new species but also examples of numerous problems of taxonomy and morphology requiring further study, including hybrids, heterochromous spores, comose rhizome scales, and specialized storage roots that have been discovered. The senior author made collecting trips to the state of Oaxaca between 1960 and 1973, resulting in 4540 collections of pteridophytes from 24 districts. Here, the authors are treating 637 species of which they have seen specimens from Oaxaca. For the taxonomic treatments, keys were prepared based on mature plants. The habitat is briefly characterized, followed by the taxon's distribution within the state.