A more thorough explanation:

The Endangered Species Act (ESA) is a law designed to protect species from becoming extinct due to economic growth and development that does not take conservation into account. The ESA aims to protect both the species and the ecosystems they depend on.

The ESA only protects species that are listed as "endangered" or "threatened." A species can be listed in two ways: the United States Fish and Wildlife Service (FWS) or National Oceanic and Atmospheric Administration (NOAA) can directly list a species through its candidate assessment program, or an individual or organization can petition the FWS or NMFS to list a species.

To be considered for listing, the species must meet one of five criteria:

1. The destruction, modification, or curtailment of its habitat or range is present or threatened.
2. It is overutilized for commercial, recreational, scientific, or educational purposes.
3. The species is declining due to disease or predation.
4. Existing regulatory mechanisms are inadequate.
5. Other natural or manmade factors are affecting its continued existence.

Potential candidate species are then prioritized, with "emergency listing" given the highest priority. Species that face a "significant risk to their wellbeing" are in this category.

Under the ESA, no federal agency may authorize, fund, or carry out any action likely to threaten or harm the existence of an endangered or threatened species (or harm their habitat). This means that federal agencies cannot consider the cost of their actions when making decisions that could harm endangered or threatened species.

Although this aspect does not apply directly to private landowners, large-scale development, logging, and mining projects usually require a federal permit, and so become subject to critical habitat regulation.

Under the ESA, no one, public or private, can "take" an endangered species of fish or wildlife. "Take" has been broadly defined to include "harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect." Furthermore, the habitat as well as the endangered animal is protected from private action. This means that private landowners cannot harm or modify the habitat of endangered or threatened species.

Although the ESA appears to provide rigid protection of endangered species, various amendments have created flexibility in the statute, resulting in less protection. Examples of these exemptions and exclusions include:

• Exemptions: In response to TVA v. Hill, an agency may now seek an exemption from the Endangered Species Committee.
• Incidental Take Permits: Under §10(a), the FWS may permit an otherwise unlawful taking if the taking is merely incidental to an otherwise lawful activity and the permit applicant has devised an acceptable habitat conservation plan (HCP).
• Safe Harbor: Under the "enhancement of survival" provision of Section §10(a)(1)(A), a landowner and FWS may enter into a voluntary agreement where the landowner agrees to alter the property to benefit or even attract a listed or proposed species in exchange for assurances that the FWS will permit future "takes" above a pre-determined level.
• The "No Surprises" rule: This is meant to give the landowner certainty and protection against "unforeseen circumstances." Should the landowner's efforts to prevent or mitigate harm to the species fall short, the government will maintain the incidental take permit and will pay for any new habitat or actions needed.

These exemptions and exclusions provide some flexibility in the ESA's protection of endangered and threatened species, but they also reduce the level of protection.

An example of the ESA in action is the case of TVA v. Hill. In this case, the courts enjoined a dam that was almost complete because opening the dam would have endangered the snail darter perch, a species listed as endangered under the ESA. This case illustrates the ESA's strict protection of endangered species, even if it means halting a project that has already cost millions of dollars.

Another example is the Babbitt v. Sweet Home case, where the Supreme Court upheld the FWS's interpretation of "harm" to include "significant habitat modification or degradation." This interpretation means that private landowners cannot harm or modify the habitat of endangered or threatened species, even if they are not directly harming the animals themselves.