The green iguana ranges over a large geographic area; it is native from southern Brazil and Paraguay as far north as Mexico.

Commonly found in captivity as a pet due to its calm disposition and bright colors, it can be very demanding to care for properly.

[6] Using nuclear and mitochondrial DNA-sequence data to explore the phylogenic history of the green iguana, scientists from El Salvador, Mexico, and the United States studied animals collected from 17 countries.

[7] The study revealed no unique mitochondrial DNA haplotypes for subspecific status, but did indicate the deep lineage divergence between Central and South American populations.

[14] The native range of the green iguana extends from southern Mexico to central Brazil, Paraguay, and Bolivia and the Caribbean; specifically Grenada, Aruba, Curaçao, Bonaire, Trinidad and Tobago, St. Lucia, St. Vincent, Montserrat, Saba and Útila.

[23] Though the species is not native to Martinique, a small wild colony of released or escaped green iguanas endures at historic Fort Saint Louis.

[24] The green iguana has been introduced from South America to Puerto Rico and is very common throughout the island, where it is considered an invasive species; in the United States, feral populations also exist in South Florida (including the Florida Keys), Hawaii, the U.S. Virgin Islands and the Rio Grande Valley of Texas.

In southern countries of their range, such as Peru, green iguanas appear bluish in colour, with bold blue markings.

[8][9] Green iguanas from the western region of Costa Rica are red, and animals of the northern ranges, such as Mexico, appear orange.

[37] Primarily herbivorous, green iguanas are presented with a special problem for osmoregulation; plant matter contains more potassium and as it has less dense nutritional content, more must be eaten to meet metabolic needs.

[40] As a result, green iguanas have developed a lateral nasal gland to supplement renal salt secretion by expelling excess potassium and sodium chlorides.

[40] Green iguanas from Guatemala and southern Mexico (which may belong to the distinct species I. rhinolopha) predominantly have small horns on their snouts between their eyes and their nostrils, whereas others do not.

[8] In addition, the dorsal spines that run along a green iguana's back are noticeably longer and thicker in males than they are in females, making the animals somewhat sexually dimorphic.

[36][41] The female green iguana gives no parental protection after egg laying, apart from defending the nesting burrow during excavation.

[41] In Panama, the green iguana has been observed sharing nest sites with American crocodiles, and in Honduras with spectacled caimans.

[41] Male green iguanas in these groups often use their own bodies to shield and protect females from predators, and it appears to be the only species of reptile to do this.

[14] If cornered by a threat, the green iguana extends and displays the dewlap under its neck, stiffens and puffs up its body, hisses, and bobs its head at the aggressor.

[14] Although they consume a wide variety of foods if offered, green iguanas are naturally herbivorous and require a precise ratio of minerals (two to one calcium to phosphorus) in their diet.

[44][45] Juvenile iguanas often eat feces from adults to acquire the essential microflora to digest their low-quality and hard-to-process vegetation-only diet.

[49] Zoologists, such as Adam Britton, believe that such a diet containing protein is unhealthy for the animal's digestive system, resulting in severe long-term health damage, including kidney failure and leading to premature death.

[8] De Vosjoli writes that captive animals have been known to survive and thrive on eating nothing but whole rodent block, or monkey chow, and one instance of romaine lettuce with vitamin and calcium supplements.

[52] In February 2012, the government of Puerto Rico proposed that the islands' iguanas, which were said to have a population of 4 million and considered to be a non-native nuisance, be eradicated and sold for meat.

[53][54] Iguanas have especially established introduced populations on islands in the Lesser Antilles, such as most of the French West Indies,[55] Sint Eustatius,[56] and Dominica.

[58][59] The green iguana is established on Oahu and Maui, Hawaii, as a feral invasive species, despite strict legislation banning the importation of any reptiles,[60][61] and in the Rio Grande Valley of Texas.

[63] They seem to be fond of eating a native endangered plant, Cordia globosa, and feeding on nickernut (Caesalpinia) a primary food plant of the endangered Miami blue butterfly (Cyclargus thomasi bethunebakeri); additionally on Marco Island, green iguanas have been observed using the burrows of the Florida burrowing owl (Athene cunicularia floridana), a species of special concern, all of which can make them more of a serious threat to Florida's ecosystem than originally believed.

[16][64] Currently, the damage green iguanas have caused has become significant and expected to increase, but controversy remains on how to deal with the problem.

[79] Green iguanas thrive only in temperatures of 79 °F (26 °C) to 95 °F (35 °C) and must have appropriate sources of UVB and UVA lighting, or else their bodies cannot produce vitamin D that promotes calcium absorption, which can result in a metabolic bone disease that can be fatal.

[80][81] Due to the potential impact of an introduced species on Hawaii's ecosystem, the state has strict regulations regarding the import and possession of green iguanas; violators can spend three years in jail and be fined up to $200,000.

[4][83] Historically, green iguana meat and eggs have been eaten as a source of protein throughout their native range,[84] and are prized for their alleged medicinal and aphrodisiac properties.

[83] In the past, there have been efforts to raise green iguanas in captivity as a food source in an attempt to encourage more sustainable land use in Panama and Costa Rica.