Bison are large bovines in the genus Bison (Greek: "wild ox" (bison) within the tribe Bovini. Two extant and numerous extinct species are recognised.

Of the two surviving species, the American bison, B. bison, found only in North America, is the more numerous. Although colloquially referred to as a buffalo in the United States and Canada, it is only distantly related to the true buffalo. The North American species is composed of two subspecies, the Plains bison, B. b. bison, and the wood bison, B. b. athabascae, which is the namesake of Wood Buffalo National Park in Canada. A third subspecies, the eastern bison (B. b. pennsylvanicus) is no longer considered a valid taxon, being a junior synonym of B. b. bison. References to "woods bison" or "wood bison" from the eastern United States refer to this subspecies, not B. b. athabascae, which was not found in the region. The European bison, B. bonasus, or wisent, or zubr, or colloquially European buffalo, is found in Europe and the Caucasus, reintroduced after being extinct in the wild.

While bison species have been traditionally classified in their own genus, modern genetics indicates that they are nested within the genus Bos, which includes, among others, cattle, yaks and gaur, being most closely related to yaks. Bison are sometimes bred with domestic cattle and produce offspring called beefalo or zubron.

Plains Bison (Bison bison bison) seen in many locations but especially Yellowstone National Park

The European bison (Bison bonasus) or the European wood bison, also known as the wisent, the zubr (/zuːbər/), or sometimes colloquially as the European buffalo, is a European species of bison. It is one of two extant species of bison, alongside the American bison. The European bison is the heaviest wild land animal in Europe, and individuals in the past may have been even larger than their modern-day descendants. During late antiquity and the Middle Ages, bison became extinct in much of Europe and Asia, surviving into the 20th century only in northern-central Europe and the northern Caucasus Mountains. During the early years of the 20th century, bison were hunted to extinction in the wild.

The species — now numbering several thousand and returned to the wild by captive breeding programmes — is no longer in immediate danger of extinction, but remains absent from most of its historical range. It is not to be confused with the aurochs (Bos primigenius), the extinct ancestor of domestic cattle, with which it once co-existed.

Besides humans, bison have few predators. In the 19th century, there were scattered reports of wolves, lions, tigers, and bears hunting bison. In the past, especially during the Middle Ages, humans commonly killed bison for their hide and meat. They used their horns to make drinking horns.

European bison were hunted to extinction in the wild in the early 20th century, with the last wild animals of the B. b. bonasus subspecies being shot in the Białowieża Forest (on today's Belarus–Poland border) in 1921. The last of the Caucasian wisent subspecies (B. b. caucasicus) was shot in the north-western Caucasus in 1927. The Carpathian wisent (B. b. hungarorum) had been hunted to extinction in the mid-1800s.

The Białowieża or lowland European bison was kept alive in captivity, and has since been reintroduced into several countries in Europe. In 1996, the International Union for Conservation of Nature classified the European bison as an endangered species, no longer extinct in the wild. Its status has improved since then, changing to vulnerable and later to near threatened.

European bison were first scientifically described by Carl Linnaeus in 1758. Some later descriptions treat the European bison as conspecific with the American bison. Three subspecies of European bison existed in the recent past, but only one, the nominate subspecies (B. b. bonasus), survives today. The ancestry and relationships of the wisent to fossil bison species remain controversial and disputed.

European Bison (Bison bonasus) - seen at the Prioksko-Terrasny Reserve, Russia

Wood Buffalo (Bison bison athabascae) - seen captive at Prioksko-Terrasny Reserve. Gift from Canada to the Soviet Union.