Most lions now live in eastern and southern Africa, and their numbers there are rapidly decreasing, with an estimated 30–50% decline over the last two decades. Currently, estimates of the African lion population range between 16,500 and 47,000 living in the wild in 2002–2004, down from early 1990s estimates that ranged as high as 100,000 and perhaps 400,000 in 1950. The cause of the decline is not well-understood, and may not be reversible. Currently, habitat loss and conflicts with humans are considered the most significant threats to the species. The remaining populations are often geographically isolated from each other, which can lead to inbreeding, and consequently, a lack of genetic diversity. Therefore the lion is considered a vulnerable species by the International Union for Conservation of Nature and Natural Resources, while the Asiatic subspecies is critically endangered. The lion population in the region of West Africa is isolated from lion populations of Central Africa, with little or no exchange of breeding individuals. The number of mature individuals in West Africa is estimated by two separate recent surveys at 850–1,160 (2002/2004). There is disagreement over the size of the largest individual population in West Africa: the estimates range from 100 to 400 lions in Burkina Faso's Arly-Singou ecosystem.
Conservation of both African and Asian lions has required the setup and maintenance of national parks and game reserves; among the best known are Etosha National Park in Namibia, Serengeti National Park in Tanzania and Kruger National Park in eastern South Africa. Outside these areas, the issues arising from lions' interaction with livestock and people usually results in the elimination of the former. In India, the last refuge of the Asiatic Lion is the 1,412 km² (558 square miles) Gir Forest National Park in western India which had about 359 lions (as of April 2006). As in Africa, numerous human habitations are close by with the resultant problems between lions, livestock, locals and wildlife officials. The Asiatic Lion Reintroduction Project plans to establish a second independent population of Asiatic Lions at the Kuno Wildlife Sanctuary in the Indian state of Madhya Pradesh. It is important to start a second population to serve as a life insurance for the last surviving Asiatic Lions and to help develop and maintain genetic diversity enabling the species to survive.
The former popularity of the Barbary Lion as a zoo animal has meant that scattered lions in captivity are likely to be descended from Barbary Lion stock. This includes twelve lions at Port Lympne Wild Animal Park in Kent, England that are descended from animals owned by the King of Morocco. Another eleven animals believed to be Barbary lions were found in Addis Ababa zoo, descendants of animals owned by Emperor Haile Selassie. WildLink International, in collaboration with Oxford University, launched their ambitious International Barbary Lion Project with the aim of identifying and breeding Barbary lions in captivity for eventual reintroduction into a national park in the Atlas Mountains of Morocco.
Following the discovery of the decline of lion population in Africa, several co-ordinated efforts involving lion conservation have been organised in an attempt to stem this decline. Lions are one species included in the Species Survival Plan, a coordinated attempt by the Association of Zoos and Aquariums to increase its chances of survival. The plan was originally started in 1982 for the Asiatic Lion, but was suspended when it was found that most North American lions were not genetically pure, having been hybridized with African lions. The African lion plan started in 1993, focusing especially on the South African subspecies, although there are difficulties in assessing the genetic diversity of captive lions, since most individuals are of unknown origins, making maintenance of genetic diversity a problem.
