The variety of species existing today is a product of 3.5 billion years of evolution, involving radiation, speciation, extinction and, more recently, the impacts of people. Current estimates of the number of species range from 5 to 30 million, with a best working estimate of 8 to 14 million; of these, only around 1.8 million have been described. There is overwhelming evidence that humans have accelerated the rate of extinction, and seriously impaired the chances of survival of an increasing number of living species. To conserve such threatened species it is essential that their status in the wild is monitored and any changes are analysed and highlighted to support conservation actions.  

Indicators that measure the status of threatened species can be used to answer specific questions, such as whether the status of individual species is changing, or to look more broadly at overall changes within taxa such as birds and amphibians.  At a national level, this indicator can be combined with others, such as change in ecosystem extent, to provide an overall picture of factors influencing the status of threatened species and to set priorities for conservation and legislation. Other relevant indicators for such analyses include changes in habitat fragmentation, coverage of protected areas and extent of productive ecosystems under sustainable management.   This indicator also compliments the messages produced by other species-based indicators such as trends in the abundance of species, and those relating to invasive species and sustainable use.

Indicators of the status of threatened species, such as the IUCN Red List Index, can also be used to help track progress towards Millennium Development Goal 7 by providing the information required for indicator 7.7 (‘a reduction in the proportion of species threatened with extinction’).  These indicators can also help countries to track progress under various agreements such as the Ramsar Convention and the Convention on Migratory Species as well as assessing the effectiveness of the Convention on Internationally Traded and Endangered Species (CITES).