The werewolf folklore found in Europe harks back to a common development during the Middle Ages, arising in the context of Christianisation, and the associated interpretation of pre-Christian mythology in Christian terms. Their underlying common origin can be traced back to Proto-Indo-European mythology, where lycanthropy is reconstructed as an aspect of the initiation of the warrior class. This is reflected in Iron Age Europe in the Tierkrieger depictions from the Germanic sphere, among others. The standard comparative overview of this aspect of Indo-European mythology is McCone (1987). Such transformations of "men into wolves" in pagan cult were associated with the devil from the early medieval perspective.

The concept of the werewolf in Western and Northern Europe is strongly influenced by the role of the wolf in Germanic paganism (e.g. the French loup-garou is ultimately a loan from the Germanic term), but there are related traditions in other parts of Europe which were not necessarily influenced by Germanic tradition, especially in Slavic Europe and the Balkans, and possibly in areas bordering the Indo-European sphere (the Caucasus) or where Indo-European cultures have been replaced by military conquest in the medieval era (Hungary, Anatolia).

In his Man into Wolf (1948), Robert Eisler tried to cast the Indo-European tribal names meaning "wolf" or "wolf-men" in terms of "the European transition from fruit gathering to predatory hunting."