This comprehensive key for identifying specimens of amphibians and reptiles in the U.S. and Canada - the first since 1983 - incorporates the wealth of scientific findings generated by molecular systematics (the study of DNA to determine genetic relationships) and simplifies identification by making geographic origin a leading factor. A dichotomous key (that is, one that gives the user only two choices at each level of morphological scrutiny), it is designed for use in college-level herpetology or vertebrate biology courses. It will be especially useful as an effective tool for teaching the principles of taxonomy and for introducing students to the systematics of amphibians and reptiles. While it can serve to identify specimens in the field, it is intended primarily as a teaching tool for classifying preserved specimens whose geographic origins are known. The dichotomous keys are supplemented by 257 line illustrations depicting the distinguishing morphological characteristics of salamanders, frogs and toads, turtles, alligators and crocodilians, amphisbaenians (wormlike lizards), lizards, and snakes.