The IUCN Red List Index (RLI) measures trends in the overall extinction risk (‘conservation status’) of sets of species, as an indicator of trends in the status of biodiversity. Extinction is a key measure of biodiversity loss that has resonance with the public and decision makers, and that has clear relevance to ecological processes and ecosystem function. The RLI is based on movement of species status through the IUCN Red List Categories, and so requires a good knowledge of these Categories and Criteria for assessment of extinction risk.
