The Red List Index is an index that measures changes in aggregate extinction risk across groups of species. It is based on the number of species in each category of extinction risk on The IUCN Red List of Threatened Species (IUCN 2015) is expressed as changes in an index ranging from 0 to 1 (for more detail on computation method, see https://unstats.un.org/wiki/display/SDGeHandbook/Indicator+15.5.1). Threatened species are those listed on The IUCN Red List of Threatened Species in the categories Vulnerable, Endangered, or Critically Endangered (i.e., species that are facing a high, very high, or extremely high risk of extinction in the wild in the medium-term future). The world’s species are impacted by a number of threatening processes, including habitat destruction and degradation, overexploitation, invasive alien species, human disturbance, pollution and climate change. This indicator can be used to assess overall changes in the extinction risk of groups of species as a result of these threats and the extent to which threats are being mitigated. The Red List Index value ranges from 1 (all species are categorized as ‘Least Concern’) to 0 (all species are categorized as ‘Extinct’), and so indicates how far the set of species has moved overall towards extinction. For additional inspiration on similar indicators, please see FAO's Forestry Policy and Institutions Working Paper 37 on "Using criteria and indicators for sustainable forest management", available at www.fao.org/publications/card/en/c/32f5155c-8f73-4114-9669-8d4b21d6972a (especially Annex 1).