The wildebeest (plural wildebeest or wildebeests), also called the gnu ( /ˈnuː/ NOO or /ˈnjuː/ NEW) is an antelope of the genus Connochaetes. It is a hooved (ungulate) mammal. Wildebeest is Dutch for "wild beast" or "wild cattle" in Afrikaans (beest = cattle), while Connochaetes derives from the Greek words konnos ("beard") and khaite ("flowing hair"). The name "gnu" originates from the Khoikhoi name for these animals, "gnou".

Gnus belong to the family Bovidae, which includes antelopes, cattle, goats, and other even-toed horned ungulates. Connochaetes includes two species, both native to Africa: the black wildebeest, or white-tailed gnu (C. gnou), and the blue wildebeest, or brindled gnu (C. taurinus). Fossil records suggest that these two species diverged about one million years ago resulting in a northern and a southern species. The blue wildebeest changed very little from the ancestor species, while the black wildebeest took on more morphological changes to adapt to a habitat of open grassland in the south. Today there are five subspecies of the blue wildebeest while the black wildebeest has no living subspecies. In East Africa, the wildebeest is the most abundant big game species, both in population and biomass.