A wet nurse is a woman who breast feeds a baby that is not her own.
A wet nurse may be employed if the birth mother of a baby is unable to breast-feed her infant for reasons such as: prescription|prescription]] or illegal)
Wet nurses have also been required following multiple births where the mother has proved incapable of adequately nursing all of the children herself.
In the past, members of higher classes would have their children wet-nursed. This is an outgrowth of an old tradition -- noblewomen would not breast-feed, and could become pregnant again sooner, to ensure an heir, if they were not nursing their infants.
While wet nurses were still in common use, some women would become pregnant and kill the child after birth to capitalize off of their lactating abilities.
Through the recent widespread availability of infant formula, wet nurses are not as necessary in developed nations and, therefore, are not common there. The use of a wet nurse is still a common practice in many developing countries.
Though it is not widely known in developed countries, a woman who has never been pregnant may produce milk. Through frequent stimulation of the areolae and nipples, a woman may begin lactating and, therefore, be able to nurse. This ability also enables women who have previously been pregnant to nurse children to whom they did not give birth.