In Irish mythology, Tír na nÓg or Tír na hÓige is one of the names for the Celtic Otherworld, or perhaps for a part of it. Tír na nÓg is best known from the tale of Oisín and Niamh.

Irish mythology is the body of myths indigenous to the island of Ireland. It was originally passed down orally in the prehistoric era. In the early medieval era, some myths were transcribed by Christian monks, who heavily altered and Christianised the myths. Irish mythology is the best-preserved branch of Celtic mythology.