The Endangered Species Act (ESA) of 1973 protects plant and animal species that are either facing extinction (endangered species) or are likely to face extinction in the foreseeable future (threatened species) and protects the ecosystems upon which they depend. The act includes provisions for listing species that need protection, designating habitat deemed critical to a listed species' survival, developing recovery plans, and protecting listed species against certain harms caused by federal and nonfederal actions. Since the act's inception, more than 1,300 species occurring in the United States or its territories have been placed on the list of threatened and endangered species. The Department of the Interior's U.S. Fish and Wildlife Service (FWS) and the Department of Commerce's National Marine Fisheries Service (NMFS)--collectively referred to as "the services"--are responsible for administration and implementation of the ESA, but all federal agencies have responsibilities for protecting species under the act. The act has long been a lightning rod for political debate about the extent to which the nation's natural resources should be protected and how best to protect them. Proponents of the act believe that it is important to preserve the unique characteristics of each species as a practical response to the impact that humans are having on the earth, and some believe that there is a moral obligation to do so. Some critics of the act deemphasize the importance of preserving every individual species and argue that doing so, in many cases, is too costly--especially when implementation of the act results in restricting the use of public and private land and resources. Others question the validity and completeness of the data used to make decisions under the act. Litigation regarding various aspects of implementation of the act has consumed considerable program resources. Over the last 10 years, we have reported on many of the major program areas of the ESA--listing, critical habitat, recovery, and the consultation process by which federal agencies ensure that their actions do not cause certain harms to listed species--and have made a number of recommendations for improvements. This report discusses recommendations that have been implemented and those that have not. Three of the five enclosures to this report contain background on the ESA, a report-by-report summary of the actions taken to implement GAO recommendations, and a list of GAO reports that discuss the ESA but do not contain recommendations related to its implementation. To conduct this follow-up review, we gathered information on agency actions from program officials and reviewed documentation where appropriate. We conducted this performance audit from August 2008 to December 2008 in accordance with generally accepted government auditing standards. Those standards require that we plan and perform the audit to obtain sufficient, appropriate evidence to provide a reasonable basis for our findings and conclusions based on our audit objectives. We believe that the evidence obtained provides a reasonable basis for our findings and conclusions based on our audit objectives.