The International Union for Conservation of Nature IUCN has prepared a Red List of Threatened Species, which classifies various species by level of endangerment. The scale ranges from low-risk to extinct. The classification is based on a combination of criteria, which include population size, the number of animals of reproductive age, the development of the population, the size of the habitat, the extent of occurrence, the fragmentation of the population, and conservation measures in place.
The IUCN updates the Red List regularly, which means that the endangerment class of a given species may improve or worsen in accordance with its situation. Not all species have been assigned a conservation class. There simply is not enough information on the situation of certain species for classes to be reliably defined.
The system can also be applied at a regional level. The Finnish Red List is coordinated by the Finnish Ministry of the Environment. It complies with the IUCN Red List Categories and Criteria and the accompanying guidelines for application.
 | Species that have been evaluated as Least Concern are widespread and abundant. They don’t appear to be facing any imminent threats. |
 | Near Threatened species are close to becoming threatened or may meet the criteria for threatened status in the near future. |
 | Vulnerable species possess a high risk of endangerment. |
 | Endangered species possess a very high risk of extinction. |
 | Critically Endangered species possess an extremely high risk of extinction. |
 | A species is Extinct in the Wild when it is known only to survive in captivity, or as a naturalized population outside its historic range. |
 | A species is Extinct when there are no known living individuals. |
Species listed as Vulnerable (VU), Endangered (EN) or Critically Endangered (CR) are concidered to be threatened.
Some species are also concidered to be Data Deficient (DD), meaning that the amount of available data related to its risk of extinction is lacking in some way.