The chicken (Gallus gallus domesticus) is a domesticated subspecies of the red junglefowl (Gallus gallus), originally native to Southeast Asia. It was first domesticated around 8,000 years ago and is one of the most common and widespread domesticated animals in the world. Chickens are primarily kept for their meat and eggs, though they are also kept as pets.

As of 2023, the global chicken population exceeds 26.5 billion, with more than 50 billion birds produced annually for consumption. Specialized breeds such as broilers and laying hens have been developed for meat and egg production, respectively. A hen bred for laying can produce over 300 eggs per year. Chickens are social animals with complex vocalizations and behaviors, and feature prominently in folklore, religion, and literature across many societies. Their economic importance makes them a central component of global animal husbandry and agriculture.

Terms for chickens include:

Chicken can mean a chick, and this was historically the meaning of the word chicken, as in William Shakespeare's play Macbeth, where Macduff laments the death of "all my pretty chickens and their dam". The usage is preserved in placenames such as the Hen and Chicken Islands. In older sources, and still often in trade and scientific contexts, chickens as a species are described as common fowl or domestic fowl.

Chickens are relatively large birds, active by day. The body is round, the legs are unfeathered in most breeds, and the wings are short. Wild junglefowl can fly; chickens and their flight muscles are too heavy to allow them to fly more than a short distance. Size and coloration vary widely between breeds. Newly-hatched chicks of both modern and heritage varieties weigh the same, about 37 g (1.3 oz). Modern varieties however grow much faster; by day 35 a Ross 708 broiler may weigh 1.8 kg (4.0 lb) as against the 1.05 kg (2.3 lb) of a heritage chicken of the same age.

Adult chickens of both sexes have a fleshy crest on their heads called a comb or cockscomb, and hanging flaps of skin on either side under their beaks called wattles; combs and wattles are more prominent in males. Some breeds have a mutation that causes extra feathering under the face, giving the appearance of a beard.

Chickens are omnivores. In the wild, they scratch at the soil to search for seeds, insects, and animals as large as lizards, small snakes, and young mice. A chicken may live for 5–10 years, depending on the breed. The world's oldest known chicken lived for 16 years.

Chickens are gregarious, living in flocks, and incubate eggs and raise young communally. Individual chickens dominate others, establishing a pecking order; dominant individuals take priority for access to food and nest sites. The concept of dominance, involving pecking, was described in female chickens by Thorleif Schjelderup-Ebbe in 1921 as the "pecking order". Male chickens tend to leap and use their claws in conflicts. Chickens are capable of mobbing and killing a weak or inexperienced predator, such as a young fox. Chickens have been thought of primarily as providers of food, but their cognition, emotions, and sociality are comparable with other birds and mammals.