• Under the ESA, a species must be listed if it is threatened or endangered due to any five specific reasons outlined.
• Petitions are official requests to list a species under the ESA.

Before a species can gain protection given by the Endangered Species Act (ESA), it needs to first be included on the federal lists of endangered and threatened wildlife and plants. A species is added to this list when the U.S. Fish and Wildlife Service (USFWS) decides that it has met the definition of endangered or threatened given under the ESA. Species can also be taken off the list or delisted when they no longer need ESA protection. Or species may have a change in status and move from threatened to endangered or vice versa (reclassified).

Under the ESA, a species must be listed if it is threatened or endangered due to any of the five reasons:

1. Current or threatened destruction, change, or decrease of its habitat or range;
2. Over-use of the species for business, leisure, scientific, or educational intentions;
3. Disease or predation;
4. Lack of present regulatory tools; and
5. Other natural or human made reasons affecting its ongoing existence.

The ESA requires that listing decisions be based only on the leading scientific and commercial data present. Economic impacts are not regarded in developing species listing decisions and are not allowed under the ESA.

Petitions are official requests to list a species under the ESA. Any interested individual can submit a drafted petition electronically or by mail. The ESA requires that USFWS create and issue certain conclusions on the petition. USFWS or the U.S. National Oceanic and Atmospheric Administration (NOAA) must make a finding within 90 days of getting a petition as to whether there is "substantial information" showing that the petitioned listing may be justified. If this initial finding is positive, USFWS runs a status review. Within one year of getting the petition, USFWS must make an additional finding that the listing is or is not justified. A positive one-year finding can be added into a proposed listing rule or, if a quick proposal is ruled out by other listing actions, the proposal may be delayed. These warranted but precluded determinations need later one-year determinations each year following until a proposed listing rule is published, or a not warranted finding is created.