The article presents theories of possible origins of lycanthropy, defined as the ability of a human to shapeshift into an animal. Because of the symbolic meaning of a wolf in the European culture, people who can turn into animals are called werewolves, while in many places of the world people metamorphoses in other creatures, like tigers or crocodiles. In European culture lycanthropy was usually perceived as an effect of magic or punishment for sins, but in shamanistic beliefs a metamorphose into an animal was conscious and beneficial to the society. The lycanthropy may be a result of a belief in reincarnation or a relic of fertility rites and brotherhoods of warriors. It is also possible that the legends of werewolves came into existence because of observation of human mental or physical illnesses.