The ferret (Mustela putorius furo) is the domesticated form of the European polecat, a mammal belonging to the same genus as the weasel, Mustela, in the family Mustelidae. Their fur is typically brown, black, white, or mixed. They have an average length of 51 cm (20 in), including a 13 cm (5.1 in) tail, weigh about 1.5–4 pounds (0.7–2 kg), and have a natural lifespan of 7 to 10 years. Ferrets are sexually dimorphic predators, with males being substantially larger than female
The history of the ferret's domestication is uncertain, like that of most other domestic animals, but it is likely that they have been domesticated for at least 2,500 years. They are still used for hunting rabbits in some parts of the world, but increasingly they are kept only as pets. Being so closely related to polecats, ferrets easily hybridize with them, and this has occasionally resulted in feral colonies of polecat–ferret hybrids that have caused damage to native fauna, especially in New Zealand. As a result, New Zealand and some other parts of the world have imposed restrictions on the keeping of ferrets. Several other mustelids also have the word ferret in their common names, including the black-footed ferret, an endangered species.