IUCN is International Union for conservation of Nature and Natural Resources with head quarters at Morges, Switzerland. It maintains a red data book (two volumes) about threatened species. The book has enlisted 277 mammals and 321 birds. India has the maximum number of threatenened species in this Rad Data Book. The number of threatened plants is over 100 e.g. Pitcher plant, Indian Podophyllum, Snow Orchid. It has classified threatened species on the basis of distribution past/present/continuous/discontinuous) abundance and quality of habitat, decline in population, biotic potential and potential value. The book has pink pages for ctitically endangered species. As soon as a species recovers, it is deleted from the pink page and entered on a green page.