Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs, or legs. An animal or machine that usually moves in a bipedal manner is known as a biped ( /ˈbaɪpɛd/), meaning "two feet" (from the Latin bi for "two" and ped for "foot"). Types of bipedal movement include walking, running, or hopping, on two appendages (typically legs).

Relatively few modern species are habitual bipeds whose normal method of locomotion is two-legged. Within mammals, habitual bipedalism has evolved multiple times, with the macropods, kangaroo mice, dipodids, springhare,hopping mice, pangolins and homininan apes as well as varius other extinct groups evolving the trait independently. In the Triassic period some groups of archosaurs (a group that includes the ancestors of crocodiles) developed bipedalism; among their descendants the dinosaurs, all the early forms and many later groups were habitual or exclusive bipeds; the birds descended from one group of exclusively bipedal dinosaurs.