The NBII Threatened and Endangered Species site provides access to data and information on threatened and endangered species managed by various federal and non-federal organizations.  Currently, the site focuses on activities in which NBII is providing a supporting role, primarily through infrastructure, to the various organizations involved. 

The Endangered Species Act of 1973 is designed to protect and recovered threatened and endangered species, as well as the ecosystems upon which they depend. According to the ESA, species may be listed as either "endangered" or "threatened."  Endangered is defined as a species that is in danger of extinction within all or a significant portion of its native range. Threatened is defined as a species that is likely to become endangered, potentially in the near term.  All species of plants and animals, except pest insects and non-native species, can be listed as endangered or threatened. Section 4 of the ESA stipulates that species may be listed only on the basis of their biological status and threats to their existence.

The Endangered Species Act is administered by two federal agencies: the Department of the Interior's U.S. Fish & Wildlife Service (FWS), and the Department of Commerce's National Marine Fisheries Service (NMFS). Terrestrial and freshwater species are managed by the FWS, while marine and most anadromous species are managed by the NMFS.

When evaluating a species for listing, these agencies analyze several factors:

•  damage to, or destruction of, the habitat upon which the species depends
•  overutizilation of the species for commercial, recreational, scientific, or educational purposes
•  predation or disease
•  inadequacy of existing protections
•  other factors, natural or human-caused, which threaten its existence 

As of March 2008, the U.S. Fish and Wildlife Service (FWS) has listed 1,925 species worldwide as either endangered or threatened, 1,351 of which are found in the United States.