IUCN Red List Categories and Criteria

The IUCN Red List Categories and Criteria were developed to assess the threatened status of species through a set of quantitative criteria. Information on the species population size and trends, distribution, habitat, ecology, threats and conservation measures is collected and then used to make an extinction risk assessment based on set defined thresholds. The categories (version 3.1) of extinction risk include:

• Extinct (EX)
• Extinct in the Wild (EW)
• Critically Endangered (CR)
• Endangered (EN)
• Vulnerable (VU)
• Near Threatened (NT)
• Least Concern (LC)
• Data Deficient (DD)

Five criteria are used to determine the extinction risk category. These include:

• Criterion A: Population reduction
• Criterion B: Geographic range in the form of either extent of occurrence or area of occupancy
• Criterion C: Small population size and decline
• Criterion D: Very small or restricted population
• Criterion E: Quanitative analysis

For detailed information: 

IUCN Red List Categories and Criteria: Version 3.1

and guidelines for use:

IUCN Red List Guidelines Version 7

Please note, the criteria have undergone a series of revisions since their initial conception, with version 3.1 released in 2001 being the most up-to-date system. Older assessments may use the Categories and Criteria version 2.3, created in 1994.

This excel file contains macros that can automatically calculate the Red List Index (RLI) and create appropriate graphs once you have entered suitable data.

The Red List Index measures overall trends in extinction risk for sets of species, based on their movements through the IUCN Red List categories of extinction risk. The RLI can be calculated for any set of species that has been assessed for the Red List at least twice. Please enable macros:

Download the Red List Index Calculator (Office 2003) 

Download the Red List Index Calculator (Office 2007)

Regional Guidelines

In 2003, IUCN developed a set of guidelines for applying the Categories and Criteria at regional levels. These guidelines 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. This is achieved by adding a second step to the assessment process, such that a species threat category (determined according to the IUCN Categories and Criteria) can be up- or downgraded, depending on the influence populations in neighbouring regions have on the population(s) being assessed.

The Regional Guidelines may be found at the following page.

Guidelines for the Application of IUCN Red List Criteria at Regional Levels

or - for the guidelines in English

For the guidance notes for national and regional Red List use:

IUCN Red List Index Guidelines for National and Regional use Version 1.1

Studies that have applied the regional guidelines are featured in the General Information section of the Library.  

Library: General Information

The Tutorials and Case Studies page can also provide help on applying the IUCN Categories and Criteria.