The IUCN Red List Categories and Criteria were developed to assess the threatened status of species through a set of quantitative criteria. The information collected on a species is used to make an extinction risk assessment based on set defined thresholds. The categories of extinction risk used at regional level (shown in the diagram) reflect those used at global level, with three differences:
The IUCN guidelines for applying the Categories and Criteria at regional level take into account the fact that in a regional assessment only a portion of a species global range (and thus only a portion of its global population) is evaluated. A second step has been integrated into the assessment process, allowing a species threat category (determined according to the IUCN Categories and Criteria) to be up- or downgraded, depending on the influence populations in neighbouring regions have on the population(s) being assessed.
The most up-to-date source for all guidelines is the IUCN Red Lists’ Categories and Criteria page. The regional Guidelines (officially in English, French and Spanish) can be found at the bottom of the page; the Red List Categories and Criteria and their associated Guidelines at the top. This page also holds further information about appropriate use of Red List data and the documentation standards for assessments and species accounts. The documentation standards must be applied to any endemic species assessment put forward for inclusion on the global list. Further translations of the Categories and Criteria and Guidelines in several other languages can be found on the IUCN’s Training pages.