The ferret is a domestic mammal of the type Mustela putorius furo. Ferrets are sexually dimorphic predators with males being substantially larger than females. They typically have brown, black, white, or mixed fur, have an average length of approximately 20 inches (51 cm) including a 5 inch (13 cm) tail,[1] weigh about 1.5–4 pounds (0.7–2 kg), and have a natural lifespan of 7 to 10 years.

Several other small, elongated carnivorous mammals belonging to the family Mustelidae (weasels) also have the word ferret in their common names, including an endangered species, the Black-footed Ferret. The ferret is a very close relative of the polecat, but it is as yet unclear whether it is a domesticated form of the European Polecat, the Steppe Polecat, or some hybrid of the two.

The history of the ferret's domestication is uncertain, like that of most other domestic animals. It is very likely that ferrets have been domesticated for at least 2,500 years. They are still used for hunting rabbits in some parts of the world today, but increasingly they are being kept simply as pets.

Being so closely related to polecats, ferrets are quite easily able to hybridize with them, and this has occasionally resulted in feral colonies of ferret polecat hybrids that have been perceived to have caused damage to native fauna, perhaps most notably in New Zealand. As a result, some parts of the world have imposed restrictions on the keeping of ferrets.

Ferreting

For millennia, the main use of ferrets was for hunting, or ferreting. With their long, lean build and inquisitive nature, ferrets are very well equipped for getting down holes and chasing rodents and rabbits out of their burrows. Caesar Augustus sent ferrets or mongooses (named "viverrae" by Plinius) to the Balearic Islands to control the rabbit plagues in 6 BC.They are still used for hunting in some countries, including the United Kingdom, where rabbits are considered a plague species by farmers. However, the practice is illegal in several countries where it is feared that ferrets could unbalance the ecology.

In England, in 1390, a law was enacted restricting the use of ferrets for hunting:

... it is ordained that no manner of layman which hath not lands to the value of forty shillings a year [the equivalent of about £1,000 in today's money] shall from henceforth keep any greyhound or other dog to hunt, nor shall he use ferrets, nets, heys, harepipes nor cords, nor other engines for to take or destroy deer, hares, nor conies, nor other gentlemen's game, under pain of twelve months' imprisonment.

Ferrets were first introduced into the New World in the 17th century, and were used extensively from 1860 until the start of World War II to protect grain stores in the American West from invading rodents.