The chicken (Gallus gallus) is a type of domesticated fowl, believed to be descended from the wild Indian and south-east Asian Red Junglefowl.
The chicken is one of the most common and wide-spread domestic animals. With a population of more than 24 billion in 2003, there are more chickens in the world than any other bird. In nature they may live for five to eleven years depending on the breed.

Domestic chickens are not capable of long distance flight, although lighter birds are generally capable of flying for short distances such as over fences or into trees (where they would naturally roost). Chickens will sometimes fly to explore their surroundings, but usually do so only to flee perceived danger. Because of the risk of escape, chickens raised in open-air pens often have one of their wings clipped by the breeder — the tips of the longest feathers on one of the wings are cut, resulting in unbalanced flight which the bird cannot sustain for more than a few meters, and it is thus discouraged from flying at all.

Chickens are gregarious birds and live together as a flock. They have a communal approach to the incubation of eggs and raising of young. Individual chickens in a flock will dominate others, establishing a "pecking order," with dominant individuals having priority for access to food and nesting locations. Removing hens or roosters from a flock causes a temporary disruption to this social order until a new pecking order is established. Adding hens, especially younger birds, to an existing flock, can lead to violence and injury.

Chickens will try to lay in nests that already contain eggs, and have been known to move eggs from neighbouring nests into their own. Some farmers use fake eggs made from plastic or stone (or golf balls) to encourage hens to lay in a particular location. The result of this behavior is that a flock will use only a few preferred locations, rather than having a different nest for every bird.

Hens can also be extremely stubborn about always laying in the same location. It is not unknown for two (or more) hens to try to share the same nest at the same time. If the nest is small, or one of the hens is particularly determined, this may result in chickens trying to lay on top of each other.

Chickens can make good companion animals and can be tamed by hand feeding, but can sometimes become aggressive. Some have advised against keeping certain breeds around young children, as the chickens can become territorial and violent. In Asia, chickens with striking plumage have long been kept for ornamental purposes, including feather-footed varieties such as the Cochin from Vietnam, the Silkie from China, and the extremely long-tailed Phoenix from Japan. Asian ornamental varieties were imported into the United States and Great Britain in the late 1800s. Distinctive American varieties of chickens have been developed from these Asian breeds. Poultry fanciers began keeping these ornamental birds for exhibition, a practice that continues today.

While some cities in the United States allow chickens as pets, the practice is not approved in all localities. The so called urban hen movement harks back to the days when chicken keeping was much more common, and involves the keeping of small groups of hens in areas where they may not be expected, such as closely populated cities and suburban areas. Individuals in rural communities commonly keep chickens for both ornamental and practical value. Some communities ban only roosters, allowing the quieter hens. Zoos sometimes use chickens instead of insecticides to control insect populations.

Chickens are generally low-maintenance. The major challenge is protecting the birds from predators such as dogs, raccoons and foxes. Chickens are usually kept in a roost at night and a pen in the day (unless they are free-range). The floor is covered with bedding such as straw or wood shavings. A bird left out at night is likely to be killed by a predator.

Eggs from household chickens can be quite different from the commercial eggs. Fresh yolks are "perky" and float above the white. The yolk color is frequently a deeper color than the pale yellow of commercially raised eggs and can at times be almost orange.