1. Endangered Species

2. The Endangered Species Act (ESA)
Law passed in 1973 by Richard Nixon on December 28th
The Act is administered by two federal agencies
The United States Fish and Wildlife Service (FWS)
The National Oceanic and Atmospheric Administration (NOAA)

3. President Richard Nixon declared current species conservation efforts to be inadequate.
He called on the 93rd United States Congress to pass comprehensive endangered species legislation.
The stated purpose of the Endangered Species Act is to protect species and also "the ecosystems upon which they depend."

4. Listing status and its abbreviations used by federal agencies:
E = endangered (Sec.3.6, Sec.4.a) - any species which is in danger of extinction throughout all or a significant portion of its range other than a species of the Class Insecta determined by the Secretary to constitute a pest.
T = threatened (Sec.3.20, Sec.4.a) - any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range

5. Other categories:
C = candidate (Sec.4.b.3) - a species under consideration for official listing
E(S/A), T(S/A) = endangered or threatened due to similarity of appearance (Sec.4.e) - a species not endagered or threatened, but so closely resembles in appearance a species which has been listed as endangered or threatened, that enforcement personnel would have substantial difficulty in attempting to differentiate between the listed and unlisted species.
XE, XN = experimental essential or non-essential population (Sec.10.j) - any population (including eggs, propagules, or individuals) of an endangered species or a threatened species released outside the current range under authorization of the Secretary. Experimental, nonessential populations of endangered species are treated as threatened species on public land, for consultation purposes, and as species proposed for listing on private land

6. Here are some websites http://www.fws.gov/endangered/