Chickens reproduce sexually, with fertilization occurring internally. The rooster, which is the male chicken, has a comb on top of its head and spurs on the back of its legs. The hen, which is the female chicken, has a smaller comb and lacks spurs.

The rooster will typically mate with several hens, and he will use his cloaca, which is a single opening that serves as the exit for both feces and reproductive material, to transfer sperm to the hen's cloaca during copulation. The sperm will then travel up the hen's oviduct and fertilize the egg as it is released.

Once fertilized, the egg will develop and be laid by the hen. The incubation period for a chicken egg is typically around 21 days, and the chick will hatch from the egg with the help of its egg tooth, which is a small protuberance on its beak that it uses to break through the shell. The newly hatched chick will be covered in down feathers and will require warmth and protection from the hen until it is able to regulate its own body temperature and fend for itself.