A giant animal in mythology is unusually large, either for their species or in relation to humans. The term giant carries some ambiguity; however, in mythology, definitions of what constitutes 'large' vary, with definitions ranging from upwards. At the upper end of this scale, they may be further subdivided into small (), medium () and large (over ). Megafauna often form one of the mythemes of a story. The narrative may revolve around a real animal or a primordial archetype of a gigantic creature, such as a dragon, sea monsters, or Jörmungandr, the Miðgarðr-Serpent.
Numerous myths and folklore exist depicting giant animals, including Australian, Greek, Native American, among others.