Sviatoslav's invasion of Bulgaria refers to a conflict beginning in 967/968 and ending in 971, carried out in the eastern Balkans, and involving the Kievan Rus', Bulgaria, and the Byzantine Empire. The Byzantines encouraged the Rus' ruler Sviatoslav to attack Bulgaria, leading to the defeat of the Bulgarian forces and the occupation of the northern and north-eastern part of the country by the Rus' for the following two years. The allies then turned against each other, and the ensuing military confrontation ended with a Byzantine victory. The Rus' withdrew and eastern Bulgaria was incorporated into the Byzantine Empire.

Kievan Rus', also known as Kyivan Rus', was a state and later an amalgam of principalities in Eastern and Northern Europe from the late 9th to the mid-13th century. The name was coined by Russian historians in the 19th century. Encompassing a variety of polities and peoples, including East Slavic, Norse, and Finnic, it was ruled by the Rurik dynasty, founded by the Varangian prince Rurik. The modern nations of Belarus, Russia, and Ukraine all claim Kievan Rus' as their cultural ancestor, with Belarus and Russia deriving their names from it, and the name Kievan Rus' derived from what is now the capital of Ukraine. At its greatest extent in the mid-11th century, Kievan Rus' stretched from the White Sea in the north to the Black Sea in the south and from the headwaters of the Vistula in the west to the Taman Peninsula in the east, uniting the East Slavic tribes.