Bears are mammals of the family Ursidae. Bears are classified as caniforms, or doglike carnivorans, with the pinnipeds being their closest living relatives. Although there are only eight living species of bear, they are widespread, appearing in a wide variety of habitats throughout the Northern Hemisphere and partially in the Southern Hemisphere. That which pertains to bears is called ursine. Bears are found in the continents of North America, South America, Europe, and Asia.

Common characteristics of modern bears include a large body with stocky legs, a long snout, shaggy hair, plantigrade paws with five nonretractile claws, and a short tail. While the polar bear is mostly carnivorous and the giant panda feeds almost entirely on bamboo, the remaining six species are omnivorous, with largely varied diets including both plants and animals.

With the exceptions of courting individuals and mothers with their young, bears are typically solitary animals. They are sometimes diurnal, but are usually active during the night (nocturnal) or twilight (crepuscular). Bears are aided by an excellent sense of smell, and despite their heavy build and awkward gait, they can run quickly and are adept climbers and swimmers. In autumn some bear species forage large amounts of fermented fruits which affects their behaviour. Bears use shelters such as caves and burrows as their dens, which are occupied by most species during the winter for a long period of sleep similar to hibernation.

Bears have been hunted since prehistoric times for their meat and fur. To this day, they play a prominent role in the arts, mythology, and other cultural aspects of various human societies. In modern times, the bear's existence has been pressured through the encroachment of their habitats and the illegal trade of bears and bear parts, including the Asian bile bear market. The IUCN lists six bear species as vulnerable or endangered, and even "least concern" species such as the brown bear are at risk of extirpation in certain countries. The poaching and international trade of these most threatened populations is prohibited, but still ongoing.

Evolutionary relationships

thumb|200px|Fossil of Cave bear (Ursus spelaeus) The Ursidae family belongs to the order Carnivora and is one of nine families in the suborder Caniformia, or "doglike" carnivorans. Bears' closest living relatives are the pinnipeds, a clade of three families: Odobenidae (the walrus), Otariidae (fur seals and sea lions), and Phocidae (true or earless seals). Bears comprise eight species in three subfamilies: Ailuropodinae (monotypic with the giant panda), Tremarctinae (monotypic with the Spectacled Bear), and Ursinae (containing six species divided into one to three genera, depending upon authority). thumb|left|Unlike other carnivora, bears have plantigrade hind feet The origins of Ursidae can be traced back to the very small and graceful Parictis that had a skull only 7 cm (3 in) long. Parictis first occur in North America in the Late Eocene (ca. 38 million years ago), but this genus did not appear in Eurasia and Africa until the Miocene. The raccoon-sized, dog-like Cephalogale, however, is widely regarded as the most primitive ursid and is ideally suited as a representative basal taxon for the family. Cephalogale first appeared during the middle Oligocene and early Miocene (approximately 20–30 million years ago) in Europe. Cephalogale gave rise to a lineage of early bears of the genus Ursavus. This genus radiated in Asia and ultimately gave rise to the first true bears (genus Ursus) in Europe, 5 million years ago. Even among its primitive species, such as C. minor, it exhibits typical ursid synapomorphic dentition such as posteriorly oriented M2 postprotocrista molars, elongated m2 molars, and a reduction of the premolars. Living members of the ursids are morphologically well defined by their hypocarnivorous (non-strictly meat-eating) dentitions, but fossil ursids include hypercarnivorous (strictly meat-eating) taxa, although they never achieved the extreme hypercarnivory seen in mustelids. Cephalogale was a mesocarnivore (intermediate meat-eater). Other extinct bear genera include Arctodus, Agriarctos, Plionarctos and Indarctos.