| Eystein I of Norway | |
|---|---|
 Early 12th century marble bust of Eystein | |
| King of Norway | |
| Reign | 1103 – 29 August 1123 |
| Predecessor | Magnus Barefoot |
| Successor | Sigurd the Crusader |
| Co-rulers | Sigurd the Crusader, Olaf Magnusson |
| Born | c. 1088 |
| Died | 29 August 1123 (aged 33–35) Hustad, Romsdal, Norway |
| Burial | |
| Spouse | Ingebjørg Guttormsdatter |
| Issue | Maria Øysteinsdatter |
| House | Hardrada |
| Father | Magnus Barefoot |
Eysteinn Magnusson (Old Norse: Eysteinn Magnússon, Norwegian: Øystein Magnusson; c. 1088 – 29 August 1123) was king of Norway (as Eystein I) from 1103 to 1123 together with his brothers Sigurd the Crusader and Olaf Magnusson, although since Olaf died before adulthood, only Eystein and Sigurd were effective rulers of the country.
While Sigurd gained fame as the "warrior king" (although owed almost exclusively to his three-year crusade to the Holy Land), Eystein was in contrast portrayed in the sagas as the "peace king" who stayed home in Norway and improved the country. As Eystein never engaged in warfare, considerably less information is written and known about him than about his brother Sigurd, despite his twenty-year-long reign, just a few years short of Sigurd. Eystein nonetheless gained the affection of his people, and was highly regarded by the saga writers for his deeds. Eystein and Sigurd's reign became the longest joint rule in Norwegian history.
Although the later saga literature narrates stereotypical accounts about the two kings, Eystein is known to have improved the infrastructure and raised buildings and churches, particularly across the coast in Western Norway and Trøndelag, from Bergen to the fishing centre of Lofoten in the north. Eystein's activities were especially centered in Bergen, which became an important international trade hub for fish at the time, helped by his construction projects. His activities in Bergen included moving the royal seat to a more central location in the city and building a new royal palace, as well as constructing churches and the Munkeliv Abbey.
Eystein died of illness in August 1123, and his brother Sigurd thereby became the sole Norwegian king.