Parrots are primarily birds of the tropics. Their distribution encompasses the tropical and southern temperate regions of the world, including Madagascar, many Pacific Islands, and the West Indies. In Asia they occur throughout almost all of India but extend northward only to the Himalayas and southern China. They are absent from Europe. In North America one species, the thick-billed parrot (Rhynchopsitta pachyrhyncha), once ranged north into the extreme southwestern United States. Prior to the early 1900s, however, the Carolina parakeet (Conuropsis carolinensis) inhabited most of the eastern United States; it was rendered extinct by human persecution. The last captive died in the Cincinnati Zoological Garden in 1914, but the last generally accepted observation in the wild was a flock seen in Florida in 1920, although it has been claimed that they existed in South Carolina until 1938. In the Southern Hemisphere a number of parrots range to Tasmania and New Zealand, and in South America one species is found on Tierra del Fuego, and they are absent from parts of extreme southern Africa.

The qualities of parrots, especially the ability of many species to imitate human sounds, make them popular as pets (pet). The African gray parrot (Psittacus erithacus) and some species of amazons (Amazona) from the New World tropics are particularly good mimics (mimicry). There is no evidence to suggest, however, that talking parrots realize what they are saying. Another appealing attribute of parrots is their display of affection, not only to others of their own species but also to humans. Pairs of many species, especially the lovebirds (Agapornis), are together almost constantly, nibbling each other's feathers with seeming affection; if one bird disappears, its mate sometimes dies, apparently of loneliness. Many parrots seem to delight in being petted and scratched, which is rare among birds. Parrots have extremely powerful jaws, however, and an indiscriminate attempt to pet them can result in a severe bite. The use of toes for climbing and food handling, in much the same manner as humans use hands, also makes parrots appealing. Their longevity, bright colours, intent gaze, ability to learn tricks, and willingness to remain on a perch instead of fluttering about contribute to the fondness people may feel for various kinds of parrots as pets. Finally, most species are vegetarians and thrive on a varied diet. This circumstance, as well as the fact that their droppings typically are dry and compact, means that parrots require little care.

In the early 1930s the importation and sale of parrots in the United States was drastically curtailed when psittacosis, or parrot fever, was traced to the birds. Caused by a respiratory virus that can infect humans, the disease is better called ornithosis, as it is by no means restricted to psittacine birds. Antibiotics reduce the severity of the disease.

The primary economic importance of parrots derives from their popularity with aviculturists. So popular are some species that at the close of the 20th century more than 90 species were threatened with extinction, and governments have found it necessary to pass laws forbidding export of the birds because wild populations are being depleted. Contributing to the problem is that, because of mistreatment en route, only a few of the many individuals captured ever reach the comparative safety of a comfortable cage. Only a few parrots, especially certain of the Australian seed-eating species, damage crops and therefore are hunted and killed.

Typically, parrots are gregarious and noisy, often forming small groups—sometimes huge flocks—flying rapidly high overhead and screeching. Their seemingly conspicuous bright colours are somewhat misleading, for a group of parrots in foliage is difficult to discern. The grassland-inhabiting parrots are nomadic and often occur in flocks of tens or even hundreds of thousands. The development of agriculture in the interior of Australia, particularly the increased availability of water, has resulted in larger populations of several species, such as the corella (Cacatua sanguinea) and the budgerigar.

The vocalizations (birdsong) of most parrots are loud, raucous screeches; generally, the larger the species, the more earsplitting the calls. The voices of some of the smaller ones include pleasant chattering and twittering notes. About a dozen different calls, each announcing a different mood, have been identified for the greater sulfur-crested cockatoo (Cacatua galerita). The amazing mimetic abilities of many parrots mentioned above are expressed only in captivity.

Parrots are monogamous. Some species breed colonially; others space themselves through the nesting habitat. Courtship and behaviour to maintain the pair bond may include vocalizations, bill-caressing, mutual preening, bowing, wing-raising, tail-spreading, and feeding of the mate.

With few exceptions, parrots nest in tree holes. Some species add nest material such as leaves, fibres, and bark strips; others lay their eggs on the floor of the cavity. Some lovebirds cut leaves into strips, which are then tucked into the feathers of the back for transportation to the nest. Several parrots, including the pygmy parrots and the orange-fronted parakeet (Aratinga canicularis), hollow out cavities in termite nests. Exceptional in the family is the monk parakeet (Myiopsitta monachus) of South America, which builds a communal stick nest in trees. Several species nest in rock crevices or earthen caves; examples include the burrowing parrot (Cyanoliseus patagonus), the kea, the night parrot, and the kakapo (Strigops habroptilus). The ground parrot (Pezoporus wallicus) lays its eggs in a shallow cup on the ground.

Parrot eggs are white and usually nearly spherical. Generally, the larger species lay only two eggs and produce one brood per year; the smaller species lay up to six or even eight or nine eggs and may breed two or three times per year. Incubation time, which generally varies directly with size, ranges from 19 to 30 days or more. Either both parents or else only the female may incubate the eggs. The young hatch bare or with very sparse down. They are altricial—that is, they are helpless and require complete parental care—and they are also nidicolous—that is, they remain in the nest for some time after hatching. The young are fed by regurgitation, typically by both parents. In some species at least, care of the young may continue for several weeks after they have left the nest.

Parrots can be distinguished from other birds by the structure of the feet and bill. Most birds have the four toes arranged with three directed forward—the inner (II), middle (III), and outer (IV)—and one backward, the hallux (I). This condition, called anisodactyl, literally means “without equal toes,” referring to the unequal arrangement. Parrots have two toes (the inner and middle) directed forward and two directed backward; this arrangement is called zygodactyl, which literally means “yoke-toed” and refers to the occurrence of toes in pairs. Zygodactyly also occurs in woodpeckers and their allies (Piciformes (piciform)), cuckoos (Cuculiformes (cuculiform)), and some other birds. The proximal (upper) bone of a bird's foot, the tarsometatarsus (commonly considered the lower leg), lies between the elevated heel joint and the toes. In parrots it is short and stout, and at least one toe is always longer. It is the characteristic short, thick tarsometatarsus—or tarsus, as the entire region is called—and the zygodactylous long, strong toes that enable parrots to climb and manipulate objects so ably. The entire foot is encased in tough skin covered with small scales.

The most distinctive morphological trait of parrots is the strongly hooked, powerful bill. Superficially the bill resembles that of the hawks and owls, but the upper and lower mandibles of parrots normally have a stronger and more uniform curve. Often the anterior edge of the lower jaw is broad and truncate. The undersurface of the upper bill usually possesses transverse or oblique filelike corrugations where the lower jaw occludes. These filelike ridges, along with the highly manipulative tongue, assist in holding seeds as the bird uses the chisel-shaped cutting edge of the lower bill to peel away a seed cover.

The use of the bill for manipulating objects, for cracking hard nuts, and as a third “foot” in climbing are all possible because of a highly kinetic (movable) upper jaw. Most living birds have such a kinetic upper jaw, which is connected to the skull dorsally by a hinge and is able to be moved independently by swinging on this hinge, but nowhere among birds is this kinesis better expressed than in parrots. The raising of the upper jaw can be described as follows: all movement of the upper jaw originates at the point of attachment between the skull and the quadrate bone, which forms the hinge between the skull and the lower jaw. Two series of bones (the quadratojugal-jugal series and the pterygoid-palatine series), both of which lie in the roof of the mouth, are situated between the quadrate and the upper jaw. When the quadrate is swung forward, the two series of bones slide forward, causing the upper jaw to swing upward on its hinge with the skull.

The short, thick, and fleshy tongue of parrots shows a variety of specializations at the tip; one found in several groups is a brushlike fringe. Primarily, the tongue functions to manipulate and hold food. Those parrots with brushlike terminal papillae (projections) on the tongue use them to hold juices, as a brush holds paint.

All parrots possess a cere, an area of soft skin surrounding the nostrils; it may be bare or covered with small, soft feathers. In adult budgerigars the cere is blue in males and tan in females.

The orbits (eye sockets) of some, but not all, parrots are ringed with bone. Other features of the parrot skeleton include a prominent keel on the sternum (breastbone), except in the flightless owl parrot of New Zealand, and a highly variable furcula (wishbone), which may be normal, weak, unfused, or absent.

Powder downs, which occur in a variety of birds, including some parrots, are specialized feathers, usually found in well-defined patches, that produce a powdery substance used to clean and waterproof the other feathers. They are well developed in cockatoos, in which they occur primarily as a pair of lateral rump patches.

Skin glands, which are abundant in mammals, are almost entirely lacking in birds, with the exception of the oil gland (preen gland). The oil produced in this gland—also known as the uropygial gland (preen gland) because of its location at the base of the tail and as the preen gland because of its function—is used, like the powder down, to clean and waterproof the feathers. Oil is squeezed from the gland, and birds either use the bill to apply it to the feathers or rub their heads directly over the gland. The nipple of the gland, which protrudes through the skin at the base of the tail dorsally, is surrounded by a tuft of feathers in parrots. Not all parrots have an oil gland; for example, it is absent from the Amazona, Brotogeris, and Pionus parrots and greatly reduced in some others.

Parrots are an ancient group of birds that probably originated in the Australian region. The oldest known fossil is that of a cockatoo from Queensland dating to the Early to Middle Miocene Epoch (23.8 to 11.2 million years ago). Despite their great diversification in size and colour, parrots of all taxa remain remarkably similar. The greatest structural diversity is exhibited by parrots from the Australo-Papuan region, but the greatest number of species occur in the New World tropics. Dispersed on a multitude of small islands, parrots have always been vulnerable to extinction, and in recent times the group has suffered increasingly in this regard. From 1680 to the early 1960s, at least 16 species disappeared entirely, and another 14 became endangered. Most of the extinct species lived on small islands or on large islands in the West Indies; only the Carolina parakeet had an extensive continental range.

The relationships of psittaciforms to other birds is still unknown. Various authors have suggested common ancestries with such groups as hawks (Falconiformes (falconiform)), owls (Strigiformes (owl)), chickenlike birds (Galliformes (galliform)), pigeons (Columbiformes (columbiform)), woodpeckers (Piciformes (piciform)), and cuckoos (Cuculiformes (cuculiform)), especially the turacos (turaco) (Musophagidae).

The family Cacatuidae was only recently distinguished clearly from Psittacidae. In turn, the Psittacidae comprises many well-defined subgroups. Lories and lorikeets (subfamily Loriinae), for example, are sometimes separated into their own family, Loriidae.