The criteria system


Conservation assessments can be carried out using a number of different criteria systems to rank species, but the most widely used system is provided by the IUCN Red List Categories and Criteria, which were developed to assess the threatened status of species through a set of objective quantitative criteria.

The IUCN Categories and Criteria

These categories and criteria, which were originally developed for use at the global level, have been adapted to allow extinction risk assessments of species at national and regional levels. Using this widely-used system has two key advantages:

1. a standardised assessment framework allowing comparability across assessments from other countries;

2. assessments of country endemics can be fed directly into the IUCN Red List of Threatened Species.

While the categories of extinction risk used reflect those used at the global level, there are two additional categories for national or regional assessments which are not used for global assessments:

  • Regionally Extinct (RE) – taxa extinct within the region but extant in other parts of the world
  • Not Applicable (NA) – for taxa not eligible for assessment at the regional level (mainly introduced taxa and vagrants
IUCN. (2012) European Red List: Species Threatened Status. [Online] Available from: [Accessed 14th May 2012]

IUCN. (2012) European Red List: Species Threatened Status. [Online] Available from: [Accessed 14th May 2012]

There is ample information on how to apply the IUCN Categories and Criteria on the IUCN Red List website. This includes:

The IUCN can provide Red List trainers to lead these workshops with national assessors, usually as four-day training workshops (though this can be amended to fit specific requirements and needs). For more information, you can contact the IUCN directly at [email protected].

Other category systems

Other category systems used are adaptations based on the IUCN system or are nationally-developed systems independent of the IUCN system (e.g. NatureServe; New Zealand Threat Classification System (NZTCS); Russian Red Data Book classification). However, using different category systems means that assessments are not comparable (for example, assessments based on rarity of species are unlikely to consistently compare to assessments of extinction risk. Using a standardised system like the IUCN Categories and Criteria means that regional assessment results are readily comparable between regions; furthermore, comparable estimates from adjacent regions are vital in order to accurately estimate extinction risk within regions (see, for example, Step 3 in the application of the IUCN Red List Categories and Criteria at the regional and national level). Using a standardised system for assessment will also lead to harmonization of data collection between regions.


Examples of the assessment process

The following links give examples of the Red Listing approach carried out in South Africa and Europe, based on the IUCN Category and Criteria system.

South Africa: Assessment Methodology for the Red List of South African Plants

Europe: The European Assessment Process for Red Lists of mammals, reptiles, amphibians, freshwater fishes, butterflies, dragonflies, and selected groups of beetles, molluscs, and vascular plants