Tylwyth Teg (Middle Welsh for "Fair Family"  Welsh pronunciation: [ˈtəlwɪθ teːg]) is the most usual term in Wales for the mythological creatures corresponding to the fairy folk of English and Continental folklore and the Irish Aos Sí. Other names for them include Bendith y Mamau ("Blessing of the Mothers"), Gwyllion and Ellyllon.
The term tylwyth teg is first attested in a poem attributed to the fourteenth-century Dafydd ap Gwilym, in which the principal character gets perilously but comically lost while going to visit his girlfriend: 'Hudol gwan yn ehedeg, | hir barthlwyth y Tylwyth Teg' ('(The) weak enchantment (now) flees, / (the) long burden of the Tylwyth Teg (departs) into the mist).
In later sources the tylwyth teg are described as fair-haired and covet golden-haired human children whom they kidnap, leaving changelings (or "crimbils") in their place. They dance and make fairy rings and they live underground or under the water. They bestow riches on those they favour but these gifts vanish if they are spoken of, and fairy maidens may become the wives of human men. These fairy wives are however still bound by traditional taboos. They must be careful to avoid touching iron or they will vanish back to their realm never to be seen by their husbands again.
As the Bendith y Mamau they are sometimes described as stunted and ugly. They ride horses in fairy rades (processions) and visit houses where bowls of milk are customarily put out for them. A changeling story tells of a woman whose three-year-old son was stolen by the fairies and she was given a threefold instruction by a "cunning man" (magician) on how to get him back. She removed the top from a raw egg and began stirring the contents, and as the changeling watched her do this certain comments he made established his otherworldly identity. She then went to a crossroads at midnight during the full moon and observed a fairy rade in order to confirm that her son was with them. Lastly she obtained a black hen and without plucking it she roasted it over a wood fire until every feather dropped off. The changeling then disappeared and her son was returned to her.
According to the folklorist Wirt Sikes the Tylwyth Teg may be divided into five general types: the Ellyllon (elves), the Coblynau (fairies of the mines), the Bwbachod (household fairies similar to brownies), the Gwragedd Annwn (female fairies of the lakes and streams) and the Gwyllion (mountain fairies more akin to hags). The ellyllon (singular ellyll) inhabit groves and valleys and are similar to English elves. Their food consists of toadstools and fairy butter (a type of fungus) and they wear digitalis bell flowers as gloves. They are ruled by Queen Mab and bring prosperity to those they favour.
- C. Robert Cargill's novel Dreams and Shadows features the Tylwyth Teg (referring to it as a Bendith Y Mamau) as a child snatcher.
- Jim Butcher's short story "Curses" set in the Harry Dresden universe has the Tylwyth Teg responsible for the Curse of the Billy Goat on the Chicago Cubs.
- Joan Aiken's 1968 novel The Whispering Mountain explains the Tylwyth Teg as a diminutive Mediterranean race who were imported to Wales as slaves to work in the mines.
- In Kelley Armstrong's fantasy novel series Cainsville the Tylwyth Teg and Annwn are the main themes, but it is not initially obvious until the later books when the history of such myths are revealed.
- Lloyd Alexander's The Chronicles of Prydain include a race of Fair Folk similar to the Tylwyth Teg (which here is the name given to their underground kingdom).
- Mercedes Lackey's novel Home from the Sea features the Tylwyth Teg as mischievous elemental sprites.
- In Michael Swanwick's fantasy novel The Iron Dragon's Daughter the Tylwyth Teg are the aristocracy of the magical world.
- Seanan McGuire's October Daye series of books features a Tylwyth Teg character as an alchemist.
- Briggs, Katharine (1976). An Encyclopedia of Fairies. Pantheon Books. pp. 21, 419. ISBN 0-394-40918-3.
- Walters, John (1828). An English and Welsh Dictionary. Clwydian-Press. p. 448.
- Geiriadur Prifysgol Cymru / A Dictionary of the Welsh Language (Cardiff: Gwasg Prifysgol Cymru, 1950–2003), s.v. tylwyth.
- Evans-Wentz, Walter (1911). The Fairy-Faith in Celtic Countries. Oxford University Press. p. 138.
- Rhys, John (1901). Celtic Folklore: Welsh and Manx. 1. Oxford University Press. pp. 262–9.
- Sikes, Wirt (1880). British Goblins: Welsh Folklore, Fairy Mythology, Legends and Traditions. Sampson Low, Marston, Searle & Rivington. pp. 12-17.
- MacKillop, James (1998). Dictionary of Celtic Mythology. Oxford: Oxford University Press. p. 368. ISBN 0-19-280120-1.
- Evans-Wentz, W. Y. (1994) . The Fairy-faith in Celtic Countries. Citadel Press. p. 576. ISBN 978-0-8065-1160-3.
- Evans, Hugh (1938). Y Tylwyth Teg. Liverpool: Gwasg Y Brython. p. 98.