Hearing in reptiles is of particular interest because of the diversity in the anatomy of the reptilian auditory system. This diversity is best illustrated in the lizard, where there is significant variation in cochlear anatomy across families. This review of the auditory physiology of reptiles will begin with a detailed discussion of the extensive physiological data available for the alligator lizard (Anguid family). These data include measurements of basilar membrane motion, intracellular hair cell responses, and single-unit activity of primary auditory-nerve fibers. Single-unit data from an Iguanid lizard will be compared to that for the alligator lizard and discussed in terms of the differences in cochlear anatomy of these two families. In addition, single-unit data for other lizards and other reptiles will be reviewed. The presentation will conclude with a comparison of auditory processing in the reptile and the mammal and will consider issues such as the tuning of individual fibers and the relationship of anatomical structure to physiological response.