This project involves production of a book summarizing information on the biology of the 178 species of amphibians and reptiles occurring in the Yucatan Peninsula (defined to include all of the Mexican states of Campeche, Yucatan, and Quintana Roo, together with northern Chiapas, eastern Tabasco, the Guatemalan Department of El Peten, and the Republic of Belize). The book will permit biologists and educated lay persons (including those species of amphibian or reptile in the Peninsula, to know its geographical distribution at a glance, and to understand its ecology, behavior, food habits, and reproductive biology. Because the Yucatan Peninsula is experiencing rapid deforestation due to lumbering activities, and to the explosive buildup of tourist facilities along the east coast, remaining wilderness areas are under ever-increasing pressure, and important decisions concerning the preservation of natural areas must be, and are being, made. The book will provide, for an important element of the vertebrate fauna, the critical information necessary to make informed decisions concerning land management, and conservation policy in this large (240,000 sq. km.) portion of the New World lowland tropics.