Chameleons or chamaeleons (family Chamaeleonidae) are a distinctive and highly specialized clade of Old World lizards with 200 species described as of June 2015.

The large number of species in the family exhibit considerable variability in their capacity to change colour.

For some, it is more of a shift of brightness (shades of brown); for others, a plethora of colour-combinations (reds, yellows, greens, blues) can be seen.

Chameleons are also distinguished by their zygodactylous feet, their prehensile tail, their laterally compressed bodies, their head casques, their projectile tongues used for catching prey, their swaying gait,[2] and in some species crests or horns on their brow and snout.

When hunting prey, the eyes focus forward in coordination, affording the animal stereoscopic vision.

Chameleons are diurnal and adapted for visual hunting of invertebrates, mostly insects, although the large species also can catch small vertebrates.

[1][3] The English word chameleon (/kəˈmiːliən/ kuh-MEEL-ee-un, /kəˈmil.jən/ kuh-MEEL-yuhn) is a simplified spelling of Latin chamaeleōn,[4] a borrowing of the Greek χαμαιλέων (khamailéōn),[5] a compound of χαμαί (khamaí) "on the ground"[6] and λέων (léōn) "lion".

Chameleons change colour by "actively tuning the photonic response of a lattice of small guanine nanocrystals in the s-iridophores".

[18] Colour change in chameleons has functions in camouflage, but most commonly in social signaling and in reactions to temperature and other conditions.

The fluorescence is derived from bones that only are covered in very thin skin and it possibly serves a signaling role, especially in shaded habitats.

Exciting the lattice increases the distance between the nanocrystals, and the skin reflects longer wavelengths of light.

The diverse speciation of chameleons has been theorized to have directly reflected the increase in open habitats (savannah, grassland, and heathland) that accompanied the Oligocene period.

[33] Daza et al. (2016) described a small (10.6 mm in snout-vent length), probably neonatal lizard preserved in the Cretaceous (Albian-Cenomanian boundary) amber from Myanmar.

The authors noted that the lizard has "short and wide skull, large orbits, elongated and robust lingual process, frontal with parallel margins, incipient prefrontal boss, reduced vomers, absent retroarticular process, low presacral vertebral count (between 15 and 17) and extremely short, curled tail"; the authors considered these traits to be indicative of the lizard's affiliation with Chamaeleonidae.

[35] This specimen was given the name Yaksha perettii in 2020, and was noted to have several convergently chameleon-like features, including adaptations for ballistic feeding.

[44] Chameleons exposed to ultraviolet light show increased social behavior and activity levels, are more inclined to bask, feed, and reproduce as it has a positive effect on the pineal gland.

All chameleons are primarily insectivores that feed by ballistically projecting their long tongues from their mouths to capture prey located some distance away.

[53] The thermal insensitivity of tongue projection thus enables chameleons to feed effectively on cold mornings prior to being able to behaviorally elevate their body temperatures through thermoregulation, when other sympatric lizards species are still inactive, likely temporarily expanding their thermal niche as a result.

[25] Chameleons primarily live in the mainland of sub-Saharan Africa and on the island of Madagascar, although a few species live in northern Africa, southern Europe (Portugal, Spain, Italy, Greece, Cyprus and Malta), the Middle East, southeast Pakistan, India, Sri Lanka, and several smaller islands in the western Indian Ocean.

[1] Chameleons are found only in tropical and subtropical regions and inhabit all kinds of lowland and mountain forests, woodlands, shrublands, savannas, and sometimes deserts, but each species tends to be a restricted to only one of a few different habitat types.

The genus Brookesia, which comprises the majority of the species in the subfamily Brookesiinae, live low in vegetation or on the ground among leaf litter.

[58] To understand the dynamics of water potential in Chameleon eggs, the consideration of exerted pressure on eggshells will be essential because the pressure of eggshells play an important role in the water relation of eggs during entire incubation period [59] The ovoviviparous species, such as the Jackson's chameleon (Trioceros jacksonii) have a five- to seven-month gestation period.

The membrane bursts and the newly hatched chameleon frees itself and climbs away to hunt for itself and hide from predators.

[65] Chameleons can change both their colours and their patterns (to varying extents) to resemble their surroundings or disrupt the body outline and remain hidden from a potential enemy's sight.

[67] Chameleons are subject to several protozoan parasites, such as Plasmodium, which causes malaria, Trypanosoma, which causes sleeping sickness, and Leishmania, which causes leishmaniasis.

[68] Chameleons are subject to parasitism by coccidia,[68] including species of the genera Choleoeimeria, Eimeria, and Isospora.

[69] Chameleons are popular reptile pets, mostly imported from African countries like Madagascar, Tanzania, and Togo.

[70] They have remained popular though which may be due to the captive-breeding in the U.S. which has increased to the point that the U.S. can fulfill its demand, and has now even become a major exporter as well.

[71] Pliny the Elder (1st century AD) also discusses chameleons in his Natural History,[72] noting their ability to change colour for camouflage.

The chameleon was featured in Conrad Gessner's Historia animalium (1563), copied from De aquatilibus (1553) by Pierre Belon.