The threatened species of organisms have been placed in the following categories-critically endangered, endangered and vulnerable. The IUCN Red list also includes information on plants and animals that are categorized as extinct or extinct in the wild and on plants and animals that are close to meet the threatened thresholds as near threatened species. Plants and animals that have been evaluated to have a low risk of extinction are classified as least concern.

• Extinct species: Extinct species include those which have disappeared from the Earth. A bird called Dodo which was found in Mauritius was killed for food and has now disappeared completely; in other words it has become extinct. Some of the animals which have become extinct are two-horne4 rhinoceros of Africa, the pink-headed duck, Himalayan quail and the golden langur.
• Critically endangered species:
  They are under the highest risk of extinction as their number has decreased drastically. Examples are Andean catfish, Abes Salamander, angular pebble Snail amongst many more.
• Endangered species:
  These species are represented by fewer individuals because of unfavourable factors. These animals can become extinct soon if the unfavourable factors are not checked. Examples are Indian rhinoceros, crocodile blue whale and the great Indian bustard.
• Vulnerable species:
  These species are most likely to become endangered if their security is not taken care of. Examples are chinkara deer, black buck and blue Pheasant amongst others.
• Near threatened species:
  These species are found in small numbers and scattered all over the world. They can easily enter the vulnerable and endangered category. Examples are golden cat, monk seal, American bison, Asiatic wild ass, tiger, shark, leopard, Jaguar, Okapi amongst many more.