Over the last two decades, the study of speciation has expanded from a modest backwater of evolutionary biology into a large and vigorous discipline. Thus, the literature on speciation, as well as the number of researchers and students working in this area, has grown explosively. Despite these developments, there has been no book-length treatment of speciation in many years. As a result, both the seasoned scholar and the newcomer to evolutionary biology had no ready guide to the recent literature on speciation - a body of work that is enormous, scattered, and increasingly technical. Although several excellent symposium volumes have recently appeared, these collections do not provide a unified, critical, and up-to-date overview of the field. 'Speciation' is designed to fill this gap.