Tylwyth Teg are a Welsh Fey court. Proudly independent, they intensely dislike to be called faerie. The Jili Ffrwtan are among their high-ranking women. Their king is Gwynn ap Nudd, and they held goats as sacred.
In Changes, Harry Dresden uses the Summoning Circle in his lab to call servants of the Tylwyth Teg, whose king Dresden is on good terms with. He was attempting to gather information regarding his daughter Maggie's location.