The Mule Deer (Odocoileus hermionus ) 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 White-tailed Deer. The two species often share natural habitats, and can be mistaken for one another. The most noticeable differences between the two is the color of their tails; the mule deer's is black tipped; the other most noticeable difference is the way in which the antlers grow; rather than growing and expanding forward the Mule Deer antlers "fork" as they grow. Mule bucks also tend to grow slightly larger than their white-tailed counterparts, and have somewhat more prominent ears.

There are two or three subspecies of mule deer:

• Cedros Island mule deer(Odocoileus hemionus cerrosensis Merriam, 1898)
• Rocky Mountain mule deer (Odocoileus hemionus hemionus Rafinesque, 1817)
• Black-tailed deer (Odocoileus hemionus hemionus or sometimes Odocoileus hemionus columbianus)