The bighorn sheep (Ovis canadensis) is a species of sheep in North America named for its large horns. These horns can weigh up to 30 pounds (14 kg), while the sheep themselves weigh up to 300 pounds (140 kg). Recent genetic testing indicates that there are three distinct subspecies of Ovis canadensis, one of which is endangered: Ovis canadensis sierrae. Sheep originally crossed to North America over the Bering land bridge from Siberia: the population in North America peaked in the millions, and the bighorn sheep entered into the mythology of Native Americans. However, by 1900 the population had crashed to several thousand. Conservation efforts (in part by the Boy Scouts) have restored the population.

Ovis canadensis is one of three species of mountain sheep in North America and Siberia; the other two species being Ovis dalli, which includes Dall Sheep and Stone's Sheep, and the Siberian snow sheep Ovis nivicola. Wild sheep crossed the Bering land bridge from Siberia during the Pleistocene (~750,000 years ago) and subsequently spread through western North America as far south as Baja California and northwestern mainland Mexico. Divergence from their closest Asian ancestor (snow sheep) occurred about 600,000 years ago. In North America, wild sheep have diverged into two extant species—Dall sheep, which occupy Alaska and northwestern Canada, and bighorn sheep, which range from southern Canada to Mexico. However, the status of these species is questionable given that hybridization has occurred between them in their recent evolutionary history.