An IUCN Red List critically endangered (CR or CE) species is one that has been classified by the International Union for Conservation of Nature as having a very high chance of becoming extinct in the wild. As of March 2026, out of 172,620 species listed on the IUCN Red List, 10,774 (about 6.2%) are critically endangered. Of these, 1,406 may already be extinct, and 64 may be extinct in the wild. More than half of all critically endangered species are plants, with 6,445 plant species (59.8%) listed in this category. There are also 4,277 animal species, 48 fungi species, and 4 chromista species listed as critically endangered.

The IUCN Red List informs the public about the conservation status of animal, fungi, and plant species. It groups species into seven categories based on factors such as where they live, how many individuals exist, and the threats they face. Each category shows a different level of risk of extinction worldwide. Critically endangered species are placed in the "Threatened" category.

The IUCN Red List does not mark a species as extinct until many targeted searches have been completed. Species that may be extinct are still listed as critically endangered. The IUCN keeps a list of "possibly extinct" and "possibly extinct in the wild" species, using a system similar to one developed by BirdLife International for these classifications.

Criteria

To be classified as critically endangered in the Red List, a species must meet any of the following conditions (A–E):

A) A significant drop in the number of individuals in the species, based on any of the following:

• A decrease of 90% or more in the population size over the past 10 years or three generations, whichever is longer. This decline must be caused by factors that are understood, reversible, and have stopped. Evidence for this decline must come from one or more of the following:
• a. Direct observation.
• b. A measure of how many individuals exist, suitable for the species.
• c. A decrease in the area where the species lives, the total area it occupies, or the quality of its habitat.
• d. Overuse of the species by humans or other factors.
• e. Effects from non-native species, mixing with other species, diseases, pollution, competitors, or parasites.

• A decrease of 80% or more in the population size over the past 10 years or three generations, whichever is longer. This decline may be ongoing, not fully understood, or not reversible. Evidence for this decline must come from one or more of the same factors listed above (a–e).

B) The species’ geographic range, measured in two ways: B1 (total area where the species is found) or B2 (area actually occupied by the species), or both:

• If the total area where the species is found is less than 100 km², and at least two of the following are true:
• a. The species’ habitat is highly broken up or exists in only one location.
• b. A continuing decline is observed, predicted, or inferred in any of the following:
• Total area where the species is found.
• Area actually occupied by the species.
• Quality of the habitat.
• Number of locations or groups of the species.
• Number of adult individuals.
• c. Extreme changes in any of the following:
• Total area where the species is found.
• Area actually occupied by the species.
• Number of locations or groups of the species.
• Number of adult individuals.

• If the area actually occupied by the species is less than 10 km², and at least two of the following are true:
• a. The species’ habitat is highly broken up or exists in only one location.
• b. A continuing decline is observed, predicted, or inferred in any of the following:
• Total area where the species is found.
• Area actually occupied by the species.
• Quality of the habitat.
• Number of locations or groups of the species.
• Number of adult individuals.
• c. Extreme changes in any of the following:
• Total area where the species is found.
• Area actually occupied by the species.
• Number of locations or groups of the species.
• Number of adult individuals.

C) If the species has fewer than 250 adult individuals, and either:
1. A decline of at least 25% in the number of adults is expected over the next 10 years or three generations, whichever is longer, or
2. A decline in the number of adults is observed, predicted, or inferred, and at least one of the following is true:
– a. The species is divided into groups where no group has more than 50 adults, or at least 90% of adults are in one group.
– b. There are extreme changes in the number of older individuals.

D) If the species has fewer than 50 adult individuals.

E) If a mathematical analysis shows that the species has a 50% or greater chance of becoming extinct in the wild within 10 years or three generations, whichever is longer.

Causes

The current extinction crisis is happening much faster than the natural rate of extinction. This is mainly due to human activities, such as climate change and the loss of biodiversity. Natural events can also cause stress on species or lead to extinction.

Right now, the biggest reason for species extinction is human actions that destroy habitats. Animals and plants depend on their habitats for survival. When habitats are destroyed, species populations decrease. Activities that cause habitat loss include pollution, urbanization, and agriculture. Another reason species become endangered is the arrival of invasive species. Invasive species move into new areas and use the resources there to outcompete native species. This can lead to the extinction of native species or make them endangered.

Species can also go extinct because of disease. When a disease spreads to a new area, it can affect native species. These species often do not have immunity to the disease, which can cause them to die.