Congress passed the Endangered Species Act (ESA) in 1973 in order to provide the means to conserve ecosystems that endangered or threatened species depended upon and to provide a program of conservation for the endangered and threatened species. Congress expressed the need to have all federal agencies seek to conserve endangered and threatened species, even though only two agencies are specifically tasked with carrying out the administration of the act. The U.S. Fish & Wildlife Service is the agency predominately tasked with administering the provisions of the ESA. The National Oceanic and Atmospheric Administration's Fisheries (also known as the National Marine Fisheries Service (NMFS)) is responsible for marine and anadromous species under the ESA. A species is classified as endangered under the ESA if it is at danger of extinction across all or a significant portion of its range. A species is classified as threatened if it is likely to become endangered within the foreseeable future. All species of plants and animals, except pest insects, are eligible for listing as either endangered or threatened. For purposes of the ESA, species includes subspecies, varieties, and distinct population segments for vertebrates.
The resources in this guide should be a starting point in your research. There are other materials available on your topic and this guide is intended to provide you with a good foundation for continuing your research into the ESA.