The American bison or simply bison, also commonly known as the American buffalo or simply buffalo, is an American species of bison that once roamed North America in vast herds. Its historical range, by 9000 BC, is described as the great bison belt, a tract of rich grassland that ran from Alaska to the Gulf of Mexico, east to the Atlantic Seaboard as far north as New York and south to Georgia and, according to some sources, further south to Florida, with sightings in North Carolina near Buffalo Ford on the Catawba River as late as 1750. It nearly became extinct by a combination of commercial hunting and slaughter in the 19th century and the introduction of bovine diseases from domestic cattle. With a population in excess of 60 million in the late 18th century, the species was down to just 541 animals by 1889. Recovery efforts expanded in the mid-20th century, with a resurgence to roughly 31,000 wild bison today, largely restricted to a few national parks and reserves. Through multiple reintroductions, the species is now also freely roaming wild in some regions in the United States, Canada, and Mexico, with it also being introduced to Yakutia in Russia.

Two subspecies or ecotypes have been described: the plains bison, smaller in size and with a more rounded hump, and the wood bison, the larger of the two and having a taller, square hump. The wood bison is one of the largest wild species of extant bovid in the world, surpassed only by the Asian gaur. Among extant land animals in North America, the bison is the heaviest and the longest, and the second tallest after the moose.

Spanning back many millennia, Native American tribes have had cultural and spiritual connections to the American bison. It is the national mammal of the United States of America.