The International Union for Conservation of Nature (IUCN) is the most widely-recognized authority on endangered species, with its Red List of Threatened Species (established in 1964) being the most comprehensive list of endangered species found worldwide.

It divides species into nine categories: Not Evaluated, Data Deficient, Least Concern, Near Threatened, Vulnerable, Endangered, Critically Endangered, Extinct in the Wild and Extinct.

Currently, there are more than 169,000 species on The IUCN Red List, with more than 47,000 species threatened with extinction, including 44% of reef building corals, 41% of amphibians, 38% of trees, 37% of sharks and rays, 34% of conifers, 26% of mammals, 26% of freshwater fishes and 12% of birds.

Endangered (EN) species on the IUCN Red List meet one or more of the following criteria:

• A 20% or higher chance of becoming extinct in the next 20 years or five generations

• 2,500 or fewer mature individuals in total

• 250 or fewer mature individuals per subpopulation

• A continuing population decline of 20% or more in five years or two generations

• An extent of occurrence (EOO) of less than 5,000 square kilometers (3,100 square miles)

• An area of occupancy (AOO) of less than 500 square kilometers (310 square miles)

• A population reduction of 70% or more over the past ten years or three generations

A species that is critically endangered is more likely to face extinction than one that’s simply endangered.

To qualify as critically endangered (CR) on the IUCN Red List, a species must meet at least one of the following criteria:

• A 50% or higher chance of becoming extinct in the next ten years or three generations

• 250 or fewer mature individuals in total

• 50 or fewer mature individuals per subpopulation

• A continuing population decline of 25% or more in three years or one generation

• An extent of occurrence (EOO) of less than 100 square kilometers (62 square miles)

• An area of occupancy (AOO) of less than 10 square kilometers (6 square miles)

• A population reduction of 70% or more over the past ten years or three generations

As of 2025, there are over 19,100 species listed as endangered on the IUCN Red List, over 6,853 of which are animals.

It's important to note that the total number of critically endangered species can fluctuate due to ongoing assessments and changes in species' conservation statuses. For the most current and detailed information, you can refer to the IUCN Red List's summary statistics.

As of 2025, there are over 10,400 species listed as critically endangered on the IUCN Red List, over 4,161 of which are animals.

Threats to endangered species could range from globe spanning issues like climate change to highly specific illnesses like the Devil Facial Tumour Disease (DFTD), a contagious cancer that has devastated Tasmanian devil populations. But a few threats are responsible for placing the overwhelming number of species on the Red List.

• The largest threat today is habitat loss and deterioration (deforestation, clearing of habitat for agriculture, industry, or urban developments).

• Climate change…

• The black market for illegal wildlife products is worth up to USD 20 billion per year, and poaching is a serious threat to animals ranging from elephants to pangolins to “scrotum” frogs.

• There is also legal exploitation of wildlife for resources, chiefly overfishing, which can wreak havoc on marine ecosystems.

• Speaking of wreaking havoc on ecosystems, invasive species — cane toads, lionfish, rats, domestic cats, etc. — put an estimated 42% of the worlds threatened or endangered species at risk.

• Diseases…

Many of the most endangered species fall victim to more than one threat on this list.