Once it has reached physical maturity at about 6 months, a hen lays eggs regardless of whether it has mated with a rooster. The egg production also occurs regardless of male participation.

If chickens mate, then a fertilized egg is laid. If the hen sits on the egg, or it is put into an incubator, it hatches into a chick. Most commercially sold eggs are unfertilized. In laying hens, about one egg is produced in a 24-hour period. The formation of an egg begins in the hen's ovary. A follicle, which eventually becomes the egg yolk, leaves the ovary and travels through a tube, the oviduct. This is where albumen, or white, forms around the follicle. In addition, in this area shell membranes and the shell itself cover the inner substances.