Critically Endangered is the highest risk category assigned by the IUCN Red List for wild species. Critically Endangered means that a species is either facing a very high risk of extinction, its numbers have decreased, or will decrease, by 80% within three generations.

As the Red List does not consider a species extinct until extensive, targeted surveys have been conducted, species which are possibly extinct are still listed as 'Critically Endangered.' A new ideal category for 'Possibly Extinct' has been suggested by BirdLife International to categorize these taxa.