A changeling, in various European legends, is the offspring of a fairy, troll, elf or other creature, left secretly in exchange for a human child. The motivation for this ranges from the desire to have a human servant, love of a human child, or malice.

The reality behind the legend is the birth of deformed or retarded children. In the old days, people believed that a troll had changed children before the parents had had time to baptize it.

One Scandinavian tradition, which today is quite horrific, is that the human mother could make the troll mother return the human child if the troll child was treated in a cruel manner. Thus, there were methods such as whipping the presumed changeling, putting it on the trash heap, or even inserting it in a heated oven. In at least one case a woman has been taken to court for having killed her child in an oven.

In certain legends it is possible to detect the changeling as he is much wiser than a human child. When detected in time, the elves have to take them back. Grimm's tales recount how a woman who suspected her child had been exchanged started to brew beer in the hull of an acorn. The changeling quoth: "now I am as old as an oak in the woods but I have never seen beer being brewed in an acorn" and disappeared.

In one Swedish fairy tale, the troll child grows up at a farm while the human child grows up among the trolls. Everyone advises the human mother to brutalize the changeling so that the trolls would change children once more. However, the woman refuses to treat the innocent but maladapted troll child cruelly and persists in treating it as if it was her own. In the end, her husband tries to burn the young troll, but the woman rescues it, so the man takes him on a walk to kill it in the forest. Somehow, he regrets his decision and saves the life of the troll. Suddenly, his own son returns and tells his father that his kindness broke the spell and liberated him. Every time someone tried to be cruel to the troll, his troll mother was about to treat the human child in the same manner.

In another Swedish fairy tale (which is depicted by the image), a princess is kidnapped by trolls and replaced with their own offspring (much against the wishes of the troll mother). The changelings grow up with their new parents, and both become beautiful young females, but they find it hard to adapt. The human girl is disgusted by her future bridegroom, a troll prince, whereas the troll girl is bored stiff by her life and by her dull future human groom. By coincidence, they both go astray into the forest upset with the conditions of their lives, and happen to pass each other without noticing it. The girl comes to the castle whereupon the queen immediately recognizes her, and the troll girl finds a troll woman who is cursing loudly as she works. The troll girl bursts out that the troll woman is much more fun than any other person she has ever seen, and her mother happily sees that her true daughter has returned. Both the human girl and the troll girl marry happily the same day.

Literary adaptations

• Roger Zelazny, Changeling (1980). The adventures of both changelings, maladapted in their respective new worlds are recounted.
• Changeling: The Dreaming The game in White Wolf Game Studio's "World of Darkness" role playing game line that stresses beauty and whimsey. Based off of traditional tales from various world cultures.