The U.S. Endangered Species Act (U.S. ESA) is the primary legislation that affords federal legal protections to threatened and endangered species in the United States, and is administered by the U.S. Fish and Wildlife Service (USFWS) (http://endangered.fws.gov/) and U.S. National Marine Fisheries Service (NMFS) (http://www.nmfs.noaa.gov/prot_res/overview/es.html). As defined by the Act, endangered refers to species that are "in danger of extinction within the foreseeable future throughout all or a significant portion of its range," while threatened refers to "those animals and plants likely to become endangered within the foreseeable future throughout all or a significant portion of their ranges." Plant species and varieties (including fungi and lichens), animal species and subspecies, and vertebrate animal populations are eligible for listing under the Act. Status under the U.S. Endangered Species Act in data provided by ALNHP is based on formal notices published by USFWS or NMFS in the Federal Register. Where names used by the USFWS differ from those used by ALNHP, ALNHP records include notes indicating under what name the USFWS lists the species and how that relates to the name used by ALNHP.

Definitions of Federal Listed Species Status Codes -
U.S. Fish and Wildlife Service

Code	Status Under the U.S. Endangered Species Act
LE	Listed Endangered - species in danger of extinction throughout all or a significant portion of their range.
LT	Listed Threatened - species likely to become an endangered species within the foreseeable future throughout all or a significant portion of their range.
PE	Proposed Endangered - the species is proposed to be listed as endangered.
PT	Proposed Threatened - the species is proposed to be listed as threatened.
PS	Partial Status - an infraspecific taxon or population has federal status but the entire species does not-- status is in only a portion of the species range.
C	Candidate - Species for which the U.S. Fish and Wildlife Service has on file enough substantial information on biological vulnerability and threat(s) to support proposals to list them as endangered or threatened. Development and publication of proposed rules on Candidate taxa are anticipated, and USFWS encourages other agencies to give consideration to such taxa in environmental planning.
XN	Nonessential Experimental Population – Experimental reintroduced population.