What is the IUCN?
The International Union for Conservation of Nature (IUCN) Red List of Threatened Species uses these official categories (version 3.1 criteria, still the current standard as of 2026):
Extinct Categories
Extinct (EX)
No reasonable doubt that the last individual has died. Exhaustive surveys of known and expected habitat have failed to record any individuals.
Extinct in the Wild (EW)
Known only to survive in cultivation, captivity, or as a naturalized population well outside its historic range. No free living individuals remain in the wild.
Threatened Categories (at risk of extinction)
Critically Endangered (CR)
Facing an extremely high risk of extinction in the wild.
(Often includes the tag Possibly Extinct or Possibly Extinct in the Wild when the species is likely already gone but not yet confirmed.)
Endangered (EN)
Facing a very high risk of extinction in the wild.
Vulnerable (VU)
Facing a high risk of extinction in the wild.
Lower Risk Categories
Near Threatened (NT)
Close to qualifying for a threatened category, or likely to qualify in the near future.
Least Concern (LC)
Widespread and abundant; does not qualify for a more serious category. (Most species fall here.)
Other Categories
Data Deficient (DD)
Inadequate information to make a direct or indirect assessment of extinction risk. This does not mean the species is not threatened. It simply means more data is needed.
Not Evaluated (NE)
Not yet assessed against the Red List criteria.
Quick Summary of Risk Levels
Extinct: Gone (EX)
Extinct in the Wild: Gone from wild (EW)
Critically Endangered: Extremely high risk (CR)
Endangered: Very high risk (EN)
Vulnerable: High risk (VU)
Near Threatened: Close to threatened (NT)
Least Concern: Low risk / widespread (LC)
Data Deficient: Insufficient data (DD)
Not Evaluated: Not assessed (NE)
Notes
Species listed as CR, EN, or VU are collectively called threatened.
Categories are based on quantitative criteria involving population size, rate of decline, geographic range, and fragmentation.
Status can change with new assessments (usually every few years for well studied species).
Official source: iucnredlist.org