The caribou is a medium-sized member of the deer family, which includes four other species of deer native to Canada: moose, elk, white-tailed deer, and mule deer. Caribou are similar to and belong to the same species as the wild and domesticated reindeer of Eurasia. The caribou is well adapted to its environment. Its short, stocky body conserves heat, its long legs help it move through snow, and its long dense winter coat provides effective insulation, even during periods of low temperature and high wind. The muzzle and tail are short and well haired.

There are eight types of caribou, each varying in size, shape, and color. Caribou have large, concave hoofs that spread widely to support the animal in snow and soft tundra. The feet also function as paddles when caribou swim. Antlers of adult males are large and massive; those of adult females are much shorter and are usually more slender and irregular. In late fall, caribou are clove-brown with a white neck, back, and feet and often have a white flank stripe. The hair of newborn calves is generally reddish-brown. Caribou in northern and southwestern Alaska are generally smaller than caribou in the Interior and in southern parts of the state.

Caribou, also called reindeer, are found in northern regions of North America, Europe, Asia, and Greenland. As summer approaches, caribou herds head north in one of the world's great large-animal migrations. They may travel more than 600 miles (965 kilometers) along well trod annual routes. At the end of their journey, they spend the summer feeding on the abundant grasses and plants of the tundra. In these rich grounds, an adult caribou can eat 12 pounds (5 kilograms) of food each day.

They wander all summer, feeding on leaves of small shrubs, aromatic plants, grasses, sedges, fungi, and lichens; in the fall, they breed. Caribou migrate north each summer in one of the greatest wildlife spectacles on Earth. Feeding mostly on grasses and plants in the summer, caribou eat lichen and mushrooms during winter.

There are a variety of predators that prey heavily on reindeer. Golden Eagles prey on young caribou. Wolverine will take newborn calves or birthing cows, as well as infirm adults. Brown Bears and sometimes even Polar bears prey on reindeer of all ages but are most likely to attack calves or sickly animals. The Gray Wolf is the most effective natural predator of adult reindeer, especially during the winter. As carrion, caribou are fed on by foxes, ravens and hawks. During the Ice Ages, they faced Dire wolves, Cave lions, American lions, Short-faced bears, Cave hyenas, Smilodons, Jaguars, Cougars, and possibly the ground sloth.

Caribou are usually quiet, but they may give a loud snort. Herds of snorting caribou may sound like pigs. Especially vocal are the bands of cows and new-born calves, constantly communicating with each other.

Caribou are the only deer in which male and females both have antlers, though only some females have them. Males lose them in the spring; females lose them when they give birth in June. aribou have large hooves that are useful tools for life in the harsh northlands. They are big enough to support the animal's bulk on snow and to paddle it efficiently through the water. The hoof's underside is hollowed out like a scoop and used for digging through the snow in search of food. Its sharp edges give the animal good purchase on rocks or ice.