In folklore, a werewolf (from Old English werwulf 'man-wolf'), or occasionally lycanthrope (from Ancient Greek λυκάνθρωπος 'wolf-human'), is an individual who can shapeshift into a wolf or therianthropic hybrid wolf–humanlike creature, either voluntarily or involuntarily due to a curse or other affliction. In modern fiction, especially film, transformations are often depicted as triggered by the full moon and transmitted by a bite or scratch from another werewolf. Early sources for belief in this ability or affliction, called lycanthropy, are Petronius (27–66) and Gervase of Tilbury (1150–1228).
The werewolf is a widespread concept in European folklore, existing in many variants, which are related by a common development of a Christian interpretation of underlying European folklore developed during the Middle Ages. From the early modern period, werewolf beliefs spread to the Western Hemisphere with colonialism. Belief in werewolves developed in parallel to the belief in witches during the late Middle Ages and the early modern period. Like the witchcraft trials as a whole, the trial of supposed werewolves emerged in what is now Switzerland, especially the Valais and Vaud, in the early 15th century and spread throughout Europe in the 16th, peaking in the 17th and subsiding by the 18th century.
