The Herpetofauna of the Mexican State of Aguascalientes is a systematic treatment of the 61 species of amphibians and reptiles known from Aguascalientes in central Mexico. This figure includes 14 species of amphibians and 47 species of reptiles, several of which are illustrated in color. This work begins with introductory sections on physiography, climate, and vegetational formations existing in the state. Color illustrations picture the range of habitat types found within the state. The next section deals with the composition and ecogeographic analysis of the herpetofauna. Identification keys for the 61 species are provided. The bulk of the work deals with accounts for each of the 61 species, which consist of a synonymy, statement of geographical range, remarks (including notes on distribution in Aguascalientes, taxonomic comments, and, for some species, notes on color in life), and a list of specimens examined. Literature records and/or additional records are also provided for some species. Two sections follow on seven species of probable occurrence in the state and twenty-six species deleted from the herpetofauna. A gazetteer of seventy-seven collecting localities is included. The work concludes with a list of 249 references pertinent to this study. Although Aguascalientes is one of the smallest states in Mexico, it encompasses a biogeographically important area containing portions of three major physiographic subdivisions of the Mexican Plateau.