A Changeling is a creature found in folklore and folk religion. It is typically described as being the offspring of a fairy, troll, elf or other legendary creature that has been secretly left in the place of a human child. Sometimes the term is also used to refer to the child who was taken. The apparent changeling could also be a stock or fetch, an enchanted piece of wood that would soon appear to grow sick and die.

The theme of the swapped child is common among medieval literature and reflects concern over infants thought to be afflicted with unexplained diseases, disorders, or developmental disabilities. A human child might be taken due to many factors: to act as a servant, the love of a human child, or malice. Most often it was thought that fairies exchanged the children.

In some rare cases, the very elderly of the Fairy people would be exchanged in the place of a human baby, and then the old fairy could live in comfort, being coddled by its human parents. Simple charms, such as an inverted coat or open iron scissors left where the child sleeps, were thought to ward them off, other measures included a constant watch over the child. Beauty in human children and young women, particularly blond hair, attracted the fairies.

In Scottish folklore, the children might be replacements for fairy children in the tithe to Hell, this is best known from the ballad of Tam Lin. Also, according to common Scottish myths, a child born with a caul (head helmet) across their face is a changeling, and of fey birth. Since most beings from Scandinavian folklore are said to be afraid of iron, Scandinavian parents often placed an iron item such as a pair of scissors or a knife on top of an unbaptized infant's cradle. It was believed that if a human child was taken in spite of such measures, the parents could force the return of the child by treating the changeling cruelly, using methods such as whipping or even inserting it in a heated oven. In at least one case, a woman was taken to court for having killed her child in an oven.

In one Swedish changeling tale, the human mother is advised to brutalize the changeling so that the trolls will return her son, but she refuses, unable to mistreat an innocent child despite knowing its nature. When her husband demands she abandon the changeling, she refuses, and he leaves her – whereupon he meets their son in the forest, wandering free. The son explains that since his mother had never been cruel to the changeling, so the troll mother had never been cruel to him, and when she sacrificed what was dearest to her, her husband, they had realized they had no power over her and released him.

In another Swedish fairy tale (which is depicted by the image), a princess is kidnapped by trolls and replaced with their own offspring against the wishes of the troll mother. The changelings grow up with their new parents, but both find it hard to adapt: the human girl is disgusted by her future bridegroom, a troll prince, whereas the troll girl is bored by her life and by her dull human future groom. Upset with the conditions of their lives, they both go astray in the forest, passing each other without noticing it. The princess 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 very same day.

In Wales the changeling child (plentyn cael (sing.), plant cael (pl.)) initially resembles the human it substitutes, but gradually grows uglier in appearance and behaviour: ill-featured, malformed, ill-tempered, given to screaming and biting. It may be of less than usual intelligence, but again is identified by its more than childlike wisdom and cunning.

Changelings are creatures known all over the world. Each country has its own tale to tell, each can be cruel or it can be helpful. Changelings are often very mischievous growing up, as they get older they tend to calm down and begin being more helpful. Changelings though do to their mischievous behavior are often depicted as evil creatures and sent by the devil to take the place of a human parents infant. Due to that many people feared changelings and often would take great measures to make sure that a Changeling never took the place of their infant.

In some cases, the Changeling grows up often being very loyal and caring to friends and family despite what they are. They often care more for their friends and family than they do themselves. Most Changelings enjoy helping as they get older, but they often feel different, out of place. A Changeling may always know, or my never know what it truly is. It is often believed that a Changeling was put in place of a very sick or dying baby so that the mother would never know the heartache of losing her child. The Changelings parents would than take the sick or dying human infant in place and keep it safe. The Changelings true parents are said to watch them as they grow, helping them along the way.