IUCN Red List of Threatened Species

Categories and key criteria

Assessments use a consistent set of categories and quantitative criteria so that evaluations are comparable across groups and regions. The main categories are:

• Extinct (EX) — no reasonable doubt that the last individual has died.
• Extinct in the Wild (EW) — survives only in cultivation, captivity or outside its historic range.
• Critically Endangered (CR), Endangered (EN), Vulnerable (VU) — progressively lower levels of threatened status based on declines in population, restricted range, small population size and probability of extinction.
• Near Threatened (NT) — close to qualifying for a threatened category.
• Least Concern (LC) — evaluated and not currently at significant risk.
• Data Deficient (DD) — insufficient information to make an assessment.
• Not Evaluated (NE) — not yet assessed under the criteria.

Criteria that trigger a threatened listing include measurable declines in population size, small or fragmented geographic range, low numbers of mature individuals, and quantitative models estimating extinction probability. These rules apply globally so that a species’ status is comparable regardless of its location.

How assessments are produced

Assessment is a collaborative process involving IUCN staff, specialist groups, taxonomic experts, regional committees and partner organizations. Data sources include published research, field surveys, museum records and expert knowledge. Assessors follow published guidelines and documentation of methods and data, and assessments undergo peer review before publication. Regional or national Red Lists may adapt IUCN criteria to local contexts while noting how the regional assessment relates to the global list; more information and guidance can be found via assessment guidelines.

Uses and importance

The Red List is widely used by conservation practitioners, government agencies, researchers, funders and international bodies. It helps prioritize species and habitats for protection, guides the allocation of limited conservation resources, supports environmental impact assessments, and provides indicators for monitoring biodiversity trends. Businesses and financial institutions also consult Red List data as part of environmental risk analysis. Policymakers use the information to shape legislation and conservation programs; practical advice and policy uses are described at policy resources.

Strengths, limitations and notable facts

The IUCN Red List is valued for its standardized methodology and broad taxonomic scope, but it has limitations. Many species remain unassessed or are listed as Data Deficient, and there is geographic and taxonomic bias toward better-studied groups such as vertebrates. Time lags occur between new threats and updated assessments. The Red List itself does not confer legal protection; instead, it provides the scientific basis that governments and organizations can use to create protected status or recovery actions. For technical details, data access and how to contribute to assessments, refer to contributor and data pages.

Examples and impact

Over decades, some species have moved to lower risk categories following targeted conservation actions, demonstrating the role of the Red List in measuring success as well as highlighting urgent needs. The list also documents extinctions and long-term declines, serving as an authoritative record of biodiversity change. Because it is updated regularly and publicly available, the IUCN Red List remains one of the most important reference tools for understanding and responding to the global biodiversity crisis.