Prior to the emergence of Kievan Rus' in the 9th century CE, the lands between the Baltic Sea and Black Sea were primarily populated by eastern Slavic tribes. In the northern region around Novgorod were the Ilmen Slavs and neighboring Krivichi, who occupied territories surrounding the headwaters of the West Dvina, Dnieper, and Volga Rivers. To their north, in the Ladoga and Karelia regions, were the Finnic Chud tribe. In the south, in the area around Kyiv, were the Poliane, a group of Slavicized tribes with Iranian origins, the Drevliane to the west of the Dnieper, and the Severiane to the east. To their north and east were the Vyatichi, and to their south was forested land settled by Slav farmers, giving way to steppelands populated by nomadic herdsmen.

Controversy persists over whether the Rus' were Varangians or Slavs, with the current scholarly consensus holding that they were an ancestrally Norse people that quickly assimilated into Slavic culture. This uncertainty is due largely to a paucity of contemporary sources. Attempts to address this question instead rely on archaeological evidence, the accounts of foreign observers, and legends and literature from centuries later. To some extent the controversy is related to the foundation myths of modern states in the region.

Nevertheless, the close connection between the Rus' and the Norse is confirmed both by extensive Scandinavian settlement in Belarus, Russia, and Ukraine and by Slavic influences in the Swedish language. Considering the linguistic arguments mounted by nationalist scholars, if the proto-Rus' were Norse, they must have quickly become nativized, adopting Slavic languages and other cultural practices.