Bison are large, even-toed ungulates in the genus Bison within the subfamily Bovinae.

There are two extant and four extinct species recognized. Of the four extinct species, three were North American: Bison antiquus, B. latifrons, and B. occidentalis. The fourth, Bison priscus, ranged across steppe environments from Western Europe, through Central Asia, and onto North America.

There are two surviving species: the American bison, Bison bison, found only in North America, is the most numerous. (It is only distantly related to the buffalo.) The North American species is composed of two subspecies, the plains bison, Bison bison bison, and the wood bison, Bison bison athabascae, which is the namesake of Wood Buffalo National Park in Canada. The European bison Bison bonasus, or wisent is found in Europe and the Caucasus, re-introduced after being extinct in the wild.

While all bison species are usually grouped into their own genus, they are sometimes included in the closely related genus Bos, together with cattle, gaur, kouprey and yaks, with which bison have a limited ability to interbreed.