A jötunn (anglicized jotunn or jotun;  /ˈjoʊtən/, /ˈjoʊtʊn/, or /ˈjɔːtʊn/; Icelandic: [ˈjœːtʏn]; from Old Norse jǫtunn /ˈjɔtunː/; often glossed as giant or ettin) is a being seen throughout Norse mythology. The Jötunn are a mythological race, separate from the Æsir and Vanir but of comparable strength and ability. As seen through a great number of texts and poems the Jötunn are often in opposition or competition to the Æsir or Vanir. A number of Jötunn intermarry with the Æsir and Vanir or interact with them in a non-hostile manner. Their otherworldly homeland is Jötunheimr, one of the nine worlds of Norse cosmology, separated from Midgard, the world of humans, by high mountains or dense forests. Other place names are also associated with them, including Niflheimr (land of ice, mist and fog occupied by Hrimthurs or Frost Giants), Utgarðr (Jötnar stronghold within the giants' realm) and Járnviðr (A heavily wooded area inhabited by troll-women who bear giants).

In Old Norse, the beings were called jǫtnar (singular jǫtunn, the regular reflex of the stem jǫtun- and the nominative singular ending -r), or risar (singular risi), in particular bergrisar ('mountain-risar'), or þursar (singular þurs), in particular hrímþursar ('rime-thurs'). Giantesses could also be known as gýgjar (singular gýgr) or íviðjur (singular íviðja).