Hyenas or hyaenas (from Greek "ὕαινα" — hýaina) are the animals of the family Hyaenidae of the feliform suborder of the Carnivora. With only four species, it is the fourth-smallest biological family in the Carnivora, and one of the smallest in the class Mammalia. Despite their low diversity, hyenas are unique and vital components to most African and some Asian ecosystems.

Although phylogenetically close to felines and viverrids, hyenas are behaviourally and morphologically similar to canines in several aspects; both hyenas and canines are nonarboreal, cursorial hunters that catch prey with their teeth rather than claws. Both eat food quickly and may store it, and their calloused feet with large, blunt, nonretractable nails are adapted for running and making sharp turns. However, the hyenas' grooming, scent marking, defecating habits, mating, and parental behaviour are consistent with the behavior of other feliforms. Although long reputed to be cowardly scavengers, hyenas, especially spotted hyenas, kill as much as 95% of the food they eat, and have been known to drive off leopards or lionesses from their kills. Hyenas are primarily nocturnal animals, but may venture from their lairs in the early-morning hours. With the exception of the highly social spotted hyena, hyenas are generally not gregarious animals, though they may live in family groups and congregate at kills.

Hyenas first arose in Eurasia during the Miocene period from viverrid-like ancestors, and developed into two distinct branches; the lightly built dog-like hyenas and the robust bone-crushing hyenas. Although the dog-like hyenas thrived 15 million years ago (with one taxon having colonised North America), they died out after a change in climate along with the arrival of canids into Eurasia. Of the dog-like hyena lineage, only the insectivorous aardwolf survived, while the bone-crushing hyenas (whose extant members are the spotted, brown and striped hyenas) became the undisputed top scavengers of Eurasia and Africa.

Hyenas feature prominently in the folklore and mythology of human cultures with which they are sympatric. Hyenas are mostly viewed with fear and contempt, as well as being associated with witchcraft, as their body parts are used as ingredients in traditional medicine. Among the beliefs held by some cultures, hyenas are thought to influence people's spirits, rob graves, and steal livestock and children.