The Endangered Species Act (ESA) is a far-reaching law that has sparked intense controversies over the use of public lands, the rights of property owners, and economic versus environmental benefits. In this volume a distinguished committee focuses on the science underlying the ESA and offers recommendations for making the act more effective. The committee provides an overview of what scientists know about extinction--and what this understanding means to implementation of the ESA. Habitat--its destruction, conservation, and fundamental importance to the ESA--is explored in detail. The book analyzes: Concepts of species--how the term "species" arose and how it has been interpreted for purposes of the ESA. Conflicts between species when individual species are identified for protection, including several case studies. Assessment of extinction risk and decisions under the ESA--how these decisions can be made more effectively. The book concludes with a look beyond the Endangered Species Act and suggests additional means of biological conservation and ways to reduce conflicts. It will be useful to policymakers, regulators, scientists, natural-resource managers, industry and environmental organizations, and those interested in biological conservation.