The Christianization of Scandinavia, as well as other Nordic countries and the Baltic countries, took place between the 8th and the 12th centuries. The realms of Denmark, Norway and Sweden established their own Archdioceses, responsible directly to the Pope, in 1104, 1154 and 1164, respectively. The conversion to Christianity of the Scandinavian people required more time, since it took additional efforts to establish a network of churches. The Sami remained unconverted until the 18th century. Newer archaeological research suggests there were Christians in Götaland already during the 9th century; it is further believed Christianity came from the southwest and moved towards the north.

Denmark was also the first of the Scandinavian countries which was Christianized, as Harald Bluetooth declared this around CE 975, and raised the larger of the two Jelling Stones. Although the Scandinavians became nominally Christian, it took considerably longer for actual Christian beliefs to establish themselves among the people in some regions, while the people were Christianized before the king in other regions. The old indigenous traditions that had provided security and structure were challenged by ideas that were unfamiliar, such as original sin, the Incarnation, and the Trinity. Archaeological excavations of burial sites on the island of Lovön near modern-day Stockholm have shown that the actual Christianization of the people was very slow and took at least 150 to 200 years, and this was a very central location in the Swedish kingdom. Thirteenth-century runic inscriptions from the merchant town of Bergen in Norway show little Christian influence, and one of them appeals to a Valkyrie.