Orangutans inhabit tropical forests. Tropical forests have little variance in temperature (around 23 degrees Celsius) and length of daylight (around 12 hours). However, rainfall varies considerably and is a primary factor as to the type of vegetation that grows in an area.

Borneo and Sumatra represent only 1.3% of Indonesia's land mass but support 10% of its known plant species, 12.5% of its mammals, and 17% of its other vertebrates (animals with backbones). Borneo alone has around 15,000 species of flowering plants, which is equivalent to the flowering plant diversity of the entire African continent.

Orangutans are classified as endangered by the World Conservation Union (IUCN) and United States Fish and Wildlife Service. Orangutans are listed in Appendix I of CITES.

A 2004 population estimate of Bornean orangutans was about 57,000.

A 2004 population estimate of Sumatran orangutans was about 7,300. This subspecies is listed as Critically Endangered by the IUCN.