Trolls in their numerous variations: from the dark beings of the Middle Ages to international film productions and the little Hobbit, all the way to the quirky rubber figures with neon-colored hair of the present day. Trolls are now omnipresent in our consciousness: from threatening creatures in fantasy literature to the harmless forest folk of Scandinavian children's books, from cute rubber figurines to the troublemakers of the internet community. Many things are commonly referred to as trolls. Even in the medieval Icelandic sagas, trolls play a prominent role as dangerous, otherworldly adversaries of humans, although their sometimes beautiful daughters could also have interesting relationships with the true heroes. Rudolf Simek sheds light on the foundations in medieval Scandinavian literature and also traces the drastic changes that the concept has undergone.