The American bison (Bison bison), also commonly known as the American buffalo, is a North American species of bison that once roamed the grasslands of North America in massive herds. Their range once roughly comprised a triangle between the Great Bear Lake in Canada's far northwest, south to the Mexican states of Durango and Nuevo León, and east along the western boundary of the Appalachian Mountains. Because of commercial hunting and slaughter in the 19th century, the bison nearly became extinct and is today restricted to a few national parks and reserves.

Two subspecies or ecotypes have been described: the plains bison (Bison bison bison), smaller in size and with a more rounded hump, and the wood bison (Bison bison athabascae) – the larger of the two and having a taller, square hump. Furthermore, it has been suggested that the plains bison consists of a northern (Bison bison montanae) and a southern subspecies, bringing the total to three. However, this is generally not supported. The wood bison is one of the largest wild species of bovid in the world, surpassed by only the the Asian gaur and wild Asian water buffalo. It is the largest extant land animal in North America.