The mule deer is a deer whose habitat is in the western half of North America. It gets its name from its large mule-like ears. Its closest relative is the black-tailed deer. The two species often share natural habitats, and can be mistaken for one another. The most noticeable differences between the two are the color of their tails and their antlers. The mule deer's tail is black tipped. Mule deer antlers "fork" as they grow rather than growing and expanding forward. Each year a buck's antlers start to grow in spring and are shed after mating season from mid-January to mid-April. Mule bucks also tend to grow somewhat larger than their white-tailed counterparts, particularly in cold climates, and have somewhat more prominent ears.

Instead of running, mule deer move with a bounding leap (stotting) with all four feet coming down together.

Adult male mule deer are called bucks, adult females are called does, and the young are called fawns.

In summer, it chiefly forages on not only herbaceous plants, but also various berries (including blackberry, huckleberry, salal, and thimbleberry). In winter, it forages on conifers (especially twigs of Douglas fir, cedar, Taxus yews, aspen, willow, dogwood, serviceberry, juniper, and sage). Year-round, it eats acorns and apples.

Mule deer prefer "edge" habitats and tend to move up or down with their preferred foods. Mule deer rarely travel far from water or forage, and tend to bed down within easy walking distance of both. Young mule deer and does tend to forage together in family groups while bucks tend to travel alone or with other bucks. Most actively foraging around dawn and dusk, they tend to bed down in protected areas mid-day, but will also forage at night in more open agricultural areas or when pressured by hunters.