The book examines Old Russian and Scandinavian sources telling about the struggle for power between the sons of the Kyiv prince Vladimir Svyatoslavich in 1015-1019. The civil strife of Yaroslav the Wise, Svyatopolk the Cursed and their brother Boris, later recognized as a saint, is described differently in ancient Russian chronicles, the lives of Boris and Gleb and the Scandinavian sagas. Source discrepancies generate many conflicting reconstructions of events. In this book, the history of the formation of ancient Russian and Scandinavian sources that have come down to us is restored, after which the information contained in them is compared with each other. As a result, the boundaries of verified historical reconstructions of the events of 1015-1019 are determined.