The World Conservation Union (IUCN) Red List Criteria are used to determine extinction risk and set numerical thresholds for qualification for three globally threatened categories.

Specific aims:  To provide a system that can be applied consistently by different people.  To improve objectivity by providing users with clear guidance on how to evaluate different factors which affect the risk of extinction.  To provide a system which will facilitate comparisons across widely different taxa.  To give people using the threatened species lists a better understanding of how individual species were classified.

Categories  EXTINCT (Ex) - taxa for which there is no reasonable doubt that the last individual has died. After exhaustive surveys in known and/or expected habitat, at appropriate times, throughout its historic range.  ENDANGERED (E) – taxa in danger of extinction and whose survival is unlikely if the casual factors continue operating. Include taxa with drastically reduced numbers and habitats.

 Vulnerable (V) – taxa believed to move into endangered category in the near future if the factors causing decline continue operating (overexploitation, habitat destruction, other environmental disturbance, numbers are abundant but are under threat from serious adverse factors).  Rare (R) – taxa with small world populations that are not at present endangered or vulnerable, but are a risk as some unexpected threat could easily cause a critical decline (usually small geographic distribution).

 Unknown (K) – taxa that are suspected but not definitely known to belong to any of the categories because of lack of information.

IUCN Mission Statement: “to influence, encourage and assist societies throughout the world to conserve the integrity and diversity of nature and to ensure that any use of natural resources is equitable and ecologically sustainable.”