The polar bear, or the sea bear (Ursus maritimus), is a member of the bear family, Ursidae; the mammalian order Carnivora; the genus Ursus. The polar bear is the largest species of this genus.

The polar bear can weigh as much as 800 kilogrammes. The average male polar bear weighs 400 to 450 kilogrammes and the average female polar bear weighs 350 to 380 kilogrammes. The male polar bear is 200 to 250 centimetres long and the female polar bear usually measures 160 to 250 centimetres. From its paws to the top of its shoulders, the polar bear stands 130 to 150 centimetres. The species has characteristically white fur.

The polar bear is the largest land carnivore and the only species of land mammals which has completely abandoned its habitat on land and moved to drifting ice floes in the Arctic Ocean. 

The polar bear normally ranges over densely packed ice, swims well and migrates seasonally. If there are favourable ice conditions, polar bears can even reach the North Pole during such migrations. However, they mainly range over the continental shelf along the fringes of the Arctic Ocean.

Polar bears are skilful hunters and are known for their good eyesight, sharp sense of smell and keen hearing. They mainly feed on two large species of Arctic seals: ringed seals and bearded seals (sea hares). Ingenious hunters, they resort to various tricks to catch seals.  For example, they stalk seals near areas of open water where the seals get out of the water to rest; they catch them in their burrows in the snow in the winter; or they stalk and attack prey from the water. Polar bears are so strong that they can also hunt for larger prey, such as walruses and beluga whales (Arctic white whales).

Polar bears are typically solitary animals and do not form social groups, although hierarchy may be established when they are forced to congregate.  They are generally peaceful when they are together.

However, adult male polar bears can pose a threat to cubs. Therefore, female polar bears tend to congregate in specific places, almost like maternity hospitals, where they dig out dens in the snow. In the winter, they hibernate for 50 to 80 days, with the longest possible period of hibernation being 106 days.

Gestation lasts about 230 to 250 days. Female polar bears give birth to one to three cubs every two or three years during a period from January to April. Newborn cubs weigh 700 to 800 grammes. Cubs are born blind with closed auditory passages and without pigmentation.  Their vision is finally developed 30 to 31 days after birth; also, at this time their auditory passages open. Teeth appear by the end of the second month when cubs start leaving their dens for short periods of time to discover the outside world. The young bears reach maturity when they are three or four years old.  

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Polar bear experts with the International Union for the Conservation of Nature (IUCN) estimate that about 20,000 to 25,000 animals live in the Arctic today, but the animals' numbers continue to decline. At a meeting held in Copenhagen in the summer of 2009, the IUCN polar bear experts listed the polar bear as a threatened species.

The ongoing decrease in the ice cover in the Arctic bodes poorly for the polar bear because this means the loss of the most suitable habitat for them. The seasonal disappearance of ice in the Arctic seas forces polar bears to move to  land and wait on the shore till the time when the ice returns, and during this time they can neither hunt nor feed in their usual way. These factors expose many polar bear populations to higher stress and render the animal much more vulnerable to negative conditions created by humans.  Due to the specifics of drifting ice and the higher rate of retreating ice in the Russian part of the Arctic, polar bears there are more exposed to stress, various risks and the threat of a dramatic reduction in their numbers.

However, global warming and the waning ice cover are not the only factors that harm and kill polar bears. Among other negative factors are pollution in the Arctic (particularly the Barents Sea) and poaching.  

The polar bear was placed on the IUCN Red List of Threatened Species and the Russian Federation's Red List of Threatened Species. In Russia, polar bear hunting is completely prohibited. It took only three decades of intensive trophy hunting in the first half of the 20^th century to push this species to the brink of extinction. Only the signing of an international five-party agreement on the polar bear in 1973 helped this animal survive. In Soviet times, the ban on polar bear hunting was effectively honoured, and there were only isolated cases of poaching, which did not seriously harm polar bear populations.  The situation drastically changed in the early 1990s when poaching became widespread again in some parts of the Arctic.

In such circumstances, it is especially important to focus on expanding and improving protection of polar bears, monitoring the condition of polar bear populations, tracking polar bear migration routes and studying the species' responses to climate changes.