The IUCN Red List of Threatened Species is a global inventory and scientific concept that assesses the extinction risk of biological species, subspecies, and populations worldwide. It was founded in 1964 by the International Union for Conservation of Nature (IUCN) to provide scientifically based information on the status of species and draw attention to the magnitude of threatened biodiversity. The problem it solved was the lack of a standardized, objective system to measure the conservation status of species, which is critical for guiding conservation action and policy.
The mechanism works by classifying species into nine groups based on quantitative criteria, such as rate of population decline, population size, geographic distribution, and probability of extinction. The nine categories range from Extinct (EX) and Extinct in the Wild (EW) to Least Concern (LC). Species classified as Critically Endangered (CR), Endangered (EN), and Vulnerable (VU) are collectively referred to as "threatened". The criteria were revised in 2001 to the current Version 3.1.
The Red List is a foundational tool that connects to several major international agreements and concepts. It is used to inform decisions under the Convention on International Trade in Endangered Species (CITES) and the Convention on Biological Diversity (CBD), including tracking progress toward the Aichi Biodiversity Targets. A recent development is the launch of the IUCN Green Status of Species in 2021, which complements the Red List by providing a standardized framework to measure species recovery and the impact of conservation efforts. The Red List Index (RLI), calculated from Red List data, is also used by the United Nations as an indicator for the Sustainable Development Goals.