We, the U.S. Fish and Wildlife Service (FWS) and the National Marine Fisheries Service (NMFS; collectively, the "Services"), finalize revisions to portions of our regulations that implement section 4 of the Endangered Species Act of 1973, as amended. The revisions to the regulations clarify, interpret, and implement portions of the Act concerning the procedures and criteria used for listing, reclassifying, and delisting species on the Lists of Endangered and Threatened Wildlife and Plants (Lists) and designating critical habitat.