Groa is a witch and practitioner of seidhr, the wife of Aurvandil the Bold.

She makes an appearance in the Prose Edda, in the context of Thor's battle with the giant Hrungnir. After Thor had despatched Hrungnir with his hammer Mjollnir, Groa was asked to help magically remove shards of Hrungnir's whetstone which had become embedded in Thor's head. Unfortunately while Groa was about her work, Thor distracted her by giving her news of her husband's whereabouts (he had earlier helped Aurvandil cross the river Elivagar), telling her that her husband was now at home. Groa's spell miscarried and the pieces of whetstone remained permanently embedded in Thor's head.

The same Groa is also the witch or Völva, summoned from beyond the grave, in the Old Norse poem Grogaldr, (a section of the Svipdagsmál), by her son Svipdag. In death she has lost none of her prophetic powers of seid, and is able to assist him in a successful conclusion of the epic task which he has been set by his cruel stepmother.