Reindeer and caribou are the only deer (Cervidae) where males, females, and calves produce antlers. Substantial growth of calf and female antler can be obtained with good nutrition. Like other deer, reindeer shed their antlers annually. New antler growth in the spring and summer is nourished by a highly vascular covering called velvet which is shed in August. Bull antler hardens (ossifies) in June and cow antler in July. The primary function of antler is for gaining social dominance. The reindeer has wide, spreading hooves, an adaptation to travel in deep snow. When walking, reindeer make a peculiar cracking noise produced by a tendon in the foot.

A member of the deer family, reindeer live in the northern parts of Europe, Asia and North America, surrounding the Arctic (the Arctic Circle). The North American varieties of reindeer are called caribou. Reindeer means "running deer" in one northern European language. They stand about four feet tall at the shoulder. Their typical color is grayish brown, but some domesticated reindeer are white.

For centuries, domesticated reindeer have served indigenous peoples including the Lapps in Norway, and the Tungus and Chukchi tribes in eastern Siberia. Reindeer have provided them with milk, butter, cheese, meat and clothing. They are also trained for riding and harnessed to pull a loaded sledge. Norway, Sweden and Finland are reindeer countries. And ever since Clement Moore wrote his heart-warming verses, "'Twas the night before Christmas," in the nineteenth century, the image of reindeer became inseparable from Saint Nicholas (Santa Claus).

While domesticated reindeer are quite popular, their wild cousins still roam the vast frozen tundra in large herds. In the wild, reindeer mainly feed on a kind of lichen called "reindeer moss." In captivity they are given a specially manufactured diet, supplemented with high quality hay.