The green peafowl (Pavo muticus) is a peafowl species native to the tropical forests of Southeast Asia and Indochina. It is the national bird of Myanmar. Formerly common throughout Southeast Asia, only a few isolated populations survive in Cambodia and adjacent areas of Vietnam. It has been listed as endangered on the IUCN Red List since 2009. This is primarily due to widespread deforestation, agriculture and loss of suitable habitat, severely fragmenting populations and contributing to an overall decline in numbers. The green peafowl is in demand for private and home aviculture and threatened by the pet trade, feather collectors and hunters for meat and targeted.

The green peafowl is a large bird in terms of overall size. The male is 1.8–3 m (5 ft 11 in – 9 ft 10 in) in total length, including its train, which measures 1.4–1.6 m (4 ft 7 in – 5 ft 3 in); the adult female is around half the total length of the breeding male at 1–1.1 m (3 ft 3 in – 3 ft 7 in) in length. It has a relatively large wingspan that averages around 1.2 m (3 ft 11 in) and can reach 1.6 m (5 ft 3 in) in big males. The green peafowl is capable of sustained (albeit energy-intensive) flight and is often observed on the wing.

Green peafowl males vocalize at their roost sites at dawn and dusk with a loud often repeated ki-wao. The female vocalizes with an equally loud "AOw-aa" call, with an emphasis on the first syllable. The males may also make a similar sound to the females.

The green peafowl has long upper-tail covert feathers. In the male, this extends up to 2 m (6 ft 7 in) and is adorned with eyespots; in the female, the coverts are green and much shorter, just covering the tail. Outside of the breeding season, however, the male's tail coverts (or train) is moulted; distinguishing the sexes during this period can be difficult unless they are observed quite up close. The neck and breast feathers (of both sexes) are highly iridescent green and resemble Chinese dragon scales. In the male, the scapular, median, and greater wing coverts are blue; the lesser coverts are green and form a triangle of scaly shoulder feathers (when the wing is closed). The secondaries are black and, in some subspecies, the tertials are brown and/or barred with a faint pattern. The female has blue lesser coverts, and lacks the triangle at the wing-shoulder. Females also have neck scales fringed with copper, as well as more barring on the back, the primaries and alula. Both sexes have crest feathers, are long-legged, heavy-winged, and long-tailed in silhouette. The crest of the female has slightly wider plumes, while those of the male are thinner but taller. The facial skin is double-striped with a whitish-blue; beside the ear is a yellow-orange crescent. The dark triangle below the eye (towards the eyebrow) is bluish-green in the male, and brown in the female. Seen from a distance, they are generally dark-coloured birds with pale vermilion- or buff-coloured primaries, which are quite visible in their peculiar flight; this action has been described as a true "flapping" flight, lacking the gliding that one associates with many birds.

The green peafowl was widely distributed in Southeast Asia in the past from southern China especially Yunnan, eastern and north-eastern India, southeastern Bangladesh, northern Myanmar, extending through Laos, and Thailand into Vietnam, Cambodia, Peninsular Malaysia, and the island of Java in Indonesia, but in Java they are only found in protected areas such as Ujung Kulon National Park and Baluran National Park. Records from northeastern India have been questioned and old records are possibly of feral birds. The ranges have reduced with habitat destruction and hunting.

Green peafowl are found in a wide range of habitats, including primary and secondary forest, both tropical and subtropical, as well as evergreen and deciduous. They may also be found amongst bamboo, on grasslands, savannas, scrub, and farmland edge. In Vietnam, the preferred habitat was found to be dry, deciduous forest close to water and away from human disturbance. In Java they are only found in savanna. Proximity to water appears to be an important factor.

The species was first classified as Pavo muticus by Carl Linnaeus, although it was previously described in Europe by Ulisse Aldrovandi as "Pavo Iaponensis" based on a Japanese painting given to the pope by the emperor of Japan. These birds were depicted as having no spurs; Linnaeus followed Aldrovandi's description. The Japanese had imported green peafowl from Southeast Asia for hundreds of years, and the birds were frequently depicted in Japanese paintings. As a result, the type locality described by Linnaeus was "Habitat in Japonia", though the species is not native to Japan (they were kept by the emperor and no longer occur). François Levaillant was one of the first Western ornithologists to see a live bird, imported from Macau to an animal collection in Cape of Good Hope. From an Indian painting, George Shaw described a peafowl native to India with a "blue head" and an "upright lanceolate crest", which he named Pavo spicifer, the spike-crested peacock. A third form of green peafowl was described in 1949 by Jean Delacour, as P. imperator, found in Indochina. From the advice of a bird dealer in Hong Kong, Delacour concluded there were three races of green peafowl, lumping P. spicifer into the species, as well. Today, most authorities recognise these three:

Delacour dismissed several aberrant specimens to be individual variations (including the type specimens for imperator originating from the Bolaven Plateau in Laos), and stated more subspecies may be recognised with further studies. However, few studies have been conducted to substantiate Delacour's classification, even though it is accepted by nearly all authorities. Some authors have suggested that the population found in Yunnan, which are traditionally classified as imperator, may be another race. Using the cytochrome b mitochondrial DNA gene, Ouyang et al. estimated the divergence period between green and Indian peafowl to be 3 million years. In the same study, they also noted there appeared to be two different forms of green peafowl in Yunnan which should be classified as distinct subspecies. A 2005 article from The Star newspaper of Malaysia stated that research indicated the Malaysian form to be identical to the Javanese form, but the study was not published and some authors dispute the result. Due to the large range of imperator in Indochina, other subspecies within its range have also been proposed, notably annamensis of Southeast Asia and yunnanensis of Yunnan.