The Arctic Fox (Alopex lagopus or Vulpes lagopus), also known as the White Fox, Polar Fox or Snow Fox, is a small fox native to Arctic regions of the Northern Hemisphere and is common throughout the Arctic tundra biome. The Greek word alopex, (ἀλώπηξ) means a fox and Vulpes is the Latin version. Lagopus is derived from Ancient Greek lago (λαγως), meaning "hare", + pous (πους), "foot" and refers to the hair on its feet. Although it is often assigned to its own genus Alopex, Mammal Species of the World, as well as genetic evidence places it in Vulpes with the majority of the other foxes.

The Arctic Fox lives in some of the most frigid extremes on the planet. Among its adaptations for cold survival are its deep, thick fur, a system of countercurrent heat exchange in the circulation of paws to retain core temperature, and a good supply of body fat. The fox has a low surface area to volume ratio, as evidenced by its generally rounded body shape, short muzzle and legs, and short, thick ears. Since less of its surface area is exposed to the Arctic cold, less heat escapes the body. Its furry paws allow it to walk on ice in search of food. The Arctic Fox has such keen hearing that it can precisely locate the position of prey under the snow. When it finds prey, it pounces and punches through the snow to catch its victim. Its fur changes color with the seasons: in the winter it is white to blend in with snow, while in the summer months it changes to brown.

The Arctic Fox tends to be active from early September to early May. The gestation period is 53 days. Litters tend to average 5-8 pups but may be as many as 25. Both the mother and the father help to raise their young. The females leave the family and form their own groups and the males stay with the family.

Foxes tend to form monogamous pairs in the breeding season. Litters are born in the early summer and the parents raise the young in a large den. Dens can be complex underground networks, housing many generations of foxes. Young from a previous year's litter may stay with the parents to help rear younger siblings. The kits are initially brownish; as they become older they turn white.

The Arctic Fox will generally eat any meat it can find, including lemmings, Arctic Hare, eggs, and carrion. Lemmings are the most common prey. A family of foxes can eat dozens of lemmings each day. During April and May the Arctic Fox also preys on Ringed Seal pups when the young animals are confined to a snow den and are relatively helpless. Fish beneath the ice are also part of its diet. If there is an overabundance of food hunted, the Arctic Fox will bury what the family cannot eat. When its normal prey is scarce, the Arctic Fox scavenges the leftovers and even feces of larger predators, such as the polar bear, even though the bears' prey includes the Arctic Fox itself.

The average length is 85.3 cm (33.6 in), with a range of 83 to 110 cm (33 to 43 in), in the male and 82.1 cm (32.3 in), with a range of 71.3 to 85 cm (28.1 to 33 in), in the female. The tail is 31 cm (12.2 in) long in the male and 30 cm (11.8 in) long in the female. It is 25–30 cm (9.8–11.8 in) high at the shoulder.[citation needed] On average males weigh 3.5 kg (7.7 lb), with a range of 3.2 to 9.4 kg (7.1 to 21 lb), while females average 2.9 kg (6.4 lb), with a range of 1.4 to 3.2 kg (3.1 to 7.1 lb).

Besides the nominate, there are four subspecies of this fox:

The Arctic Fox has a circumpolar range, meaning that it is found throughout the entire Arctic, including the outer edges of Greenland, Russia, Canada, Alaska, and Svalbard, as well as in Subarctic and alpine areas, such as Iceland and mainland alpine Scandinavia. The conservation status of the species is good, except for the Scandinavian mainland population. It is acutely endangered there, despite decades of legal protection from hunting and persecution. The total population estimate in all of Norway, Sweden and Finland is a mere 120 adult individuals.

The Arctic Fox is the only native land mammal to Iceland. It came to the isolated North Atlantic island at the end of the last ice age, walking over the frozen sea.

The abundance of the Arctic Fox species tends to fluctuate in a cycle along with the population of lemmings. Because the fox reproduces very quickly and often dies young, population levels are not seriously impacted by trapping. The Arctic Fox has, nonetheless, been eradicated from many areas where humans are settled.