The IUCN Red List, explained simply
Critically Endangered, Vulnerable, Least Concern: these terms appear on every one of our species pages. They come from the Red List of the International Union for Conservation of Nature (IUCN), the global reference on extinction risk. Here is how to read it.
The nine categories, from most to least severe
- Extinct (EX) Extinct There is no reasonable doubt that the last individual has died.
- Extinct in the Wild (EW) Extinct The species survives only in captivity, or in populations introduced well outside its original range.
- Critically Endangered (CR) Threatened Extremely high risk of extinction in the wild.
- Endangered (EN) Threatened Very high risk of extinction in the wild.
- Vulnerable (VU) Threatened High risk of extinction in the wild.
- Near Threatened (NT) Lower risk Close to the thresholds for a threatened category, or likely to reach them in the near future.
- Least Concern (LC) Lower risk Does not meet any of the threatened criteria. Often a widespread and abundant species.
- Data Deficient (DD) Not classified Not enough information to assess the risk. This does not mean the species is doing well.
- Not Evaluated (NE) Not classified The species has not yet been assessed against the IUCN criteria.
What is the Red List?
The Red List of Threatened Species is maintained by the IUCN, an international organization whose members include governments, public agencies and NGOs. Scientists around the world assess species one by one, using shared criteria. At the update of 9 July 2026, 175,909 species had been assessed and 49,505 were listed as threatened.
The nine categories
The categories range from Extinct to Least Concern. Three of them make up the threatened species: Critically Endangered, Endangered and Vulnerable. Two separate categories mean that we simply don’t know: Data Deficient and Not Evaluated.
What Critically Endangered means
Critically Endangered (CR) is the most serious category short of extinction. A species is listed as CR if it meets at least one of the following five criteria, simplified here:
| Criterion | What it measures | Threshold for Critically Endangered (simplified) |
|---|---|---|
| A | A rapid population decline | A decline of at least 80% over 10 years or 3 generations (at least 90% if the causes have stopped and are understood) |
| B | A tiny geographic range | A range under 100 km², or under 10 km² actually occupied, plus fragmentation, ongoing decline or extreme fluctuations |
| C | A small, declining population | Fewer than 250 adults, with an ongoing decline |
| D | An extremely small population | Fewer than 50 adults |
| E | A risk analysis | At least a 50% chance of extinction in the wild within 10 years or 3 generations |
Thresholds are less strict for Endangered and Vulnerable. The full, more detailed criteria are published by the IUCN.
One important point: the criteria count mature individuals able to breed, not every animal. That is why IUCN figures sometimes differ from census counts, which include young animals too.
How to read an assessment
Each Red List entry gives the category, the criteria used, the population trend (increasing, stable, decreasing or unknown), the threats and the conservation measures in place. It also shows the year of the assessment.
Why the date matters
An assessment is a snapshot taken at a given moment. Some of our ten species were last assessed by the IUCN more than ten years ago: the ploughshare tortoise in 2008, the Devils Hole pupfish in 2014. Since then, their situation may have changed, for better or for worse.
That is why this site always shows two dates: the year of the IUCN assessment and the year of the most recent population figure we could find, with its source. Each species page also shows the date on which we checked the data.
Moving up or down the list
A species can change category. It moves up when its situation gets worse, and down when it improves. Downlistings to a less serious category are the best proof that conservation works. Discover some of these success stories.
Sources
- IUCN Red List Categories and Criteria, Version 3.1, Second edition, IUCN (2012), accessed .
- Desert frog, deep sea molluscs among remarkable species at risk – IUCN Red List, IUCN (press release, 9 July 2026), accessed .
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