small, graceful Eurasian deer of the family Cervidae (order Artiodactyla (artiodactyl)). There are two species of roe deer: the European, or western, roe deer (Capreolus capreolus) and the larger Siberian roe deer (C. pygargus). Despite their Old World distribution, roe deer are more closely related to New World deer than to Old World deer. They are well adapted to cold environments, and they range from northern Europe and Asia into the high mountains of Central Asia, and south to Spain.

Roe deer are adapted to the forest edge. They are masters at exploiting the ecological opportunities caused by wild fires and floods. They also take advantage of human landscape disturbances and thrive when given a modicum of care and management. They are a popular game animal and are prized for their tasty venison. Roe deer are short-winded runners and expert hiders in thickets. When alarmed, the roe deer barks.

Roe deer have a very unusual reproduction biology, based on using the vegetation pulse of summer to pay directly for the high cost of rutting. Other northern deer, such as the red deer, use the summer's vegetation to store fat, which is used up later during the fall rutting period. The roe buck, however, foregoes costly fattening, forms a territory that overlaps the ranges of two or more females, and breeds these in late July or early August. For so small-bodied a deer, however, this poses a dilemma, because small deer have short gestation periods. If gestation commenced right after breeding, then fawns would be born about 150 days later, in December, in the midst of winter. For fawns to survive and for females to support lactation, fawns must be born in late May, shortly after spring vegetation begins to grow. The roe deer solves this problem through delayed implantation, in which the fertilized egg, after forming a blastocyst, remains inactive in the uterus until the beginning of January. At that time the egg implants in the uterus and develops into a fawn, which is born in late May to early June, some 276–295 days after mating.

Roe deer have a high birth rate and often bear two (sometimes three) spotted fawns. Young roe deer are dispersed by adults, and yearlings look for living space on their own.