Each year, the U.S. Fish and Wildlife Service (or the National Marine Fisheries Service for marine species) publishes a “notice of review” in the Federal Register listing animal “candidate” species being considered for endangered or threatened status one year and plant candidates the next year. Sometimes, states, citizens or others may petition the agencies to list a species. When that happens, the agencies evaluate the petition to determine whether a listing may be warranted.

After a series of procedural steps designed to ensure public participation, the appropriate secretary (secretary of Interior or Commerce) decides whether to list the species based on the best scientific information available. By law, listing decisions must be based solely on the best available biological data. (This is the only place where the act expressly prohibits economic factors to be considered.)

When a species is proposed for listing as endangered or threatened, areas of habitat believed essential to its conservation may be proposed for designation as “critical habitat.” The service may sometimes find formal designations of critical habitat not prudent because disclosing the exact location of a rare species may make it more vulnerable to collectors, curiosity seekers or vandals. Designation may also be postponed if the needed information is not available. As a practical matter, critical habitat has not been designated for most listed species.

The appropriate secretary must develop recovery plans outlining the agency’s strategy and recommendations to assist the species’ recovery.

The appropriate secretary must cooperate with the states in conserving protected species and enter into cooperative agreements to assist states in their endangered species programs.

If their actions may affect a listed species, federal agencies must ensure that those actions (including those regulating private activities) are “not likely to jeopardize the continued existence” of any endangered or threatened species, or to adversely modify or destroy designated critical habitat.

Proponents of a particular action may apply for an exemption for that action (rather than for a species) from the act. A committee of six specified federal officials and a representative of each affected state must decide whether to allow a project to proceed despite future harm to a species; at least five votes are required to pass an exemption.


An endangered species is one that is in danger of extinction throughout all or a significant portion of its range.

A threatened species is one that is likely to become endangered within the foreseeable future.

— Source: U.S. Fish and Wildlife Service; Congressional Research Service