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 instigate the Rus' ruler Sviatoslav to attack Bulgaria, leading to the collapse of the Bulgarian state and the occupation of much of the country by the Rus'.

The ensuing direct military confrontation between the Rus' and Byzantium ends with a Byzantine victory.

The Rus' withdraw and eastern Bulgaria is incorporated into the Byzantine Empire.In 927, a peace treaty is signed between Bulgaria and Byzantium that ends many years of warfare and begins forty years of peace.

Both states prosper during this interlude, but the balance of power gradually shifts in favor of the Byzantines, who make great territorial gains against the Abbasid Caliphate in the East and succeed in establishing a web of alliances that surround Bulgaria.

By 965/966, the warlike new Byzantine emperor Nikephoros II Phokas refusedsto renew the annual tribute that is part of the peace agreement and declares war on Bulgaria.

Preoccupied with his campaigns in the East, Nikephoros resolves to fight the war by proxy, and invites the Rus' ruler Sviatoslav to invade Bulgaria.Sviatoslav's subsequent campaign greatly exceeds the expectations of the Byzantines, who had regarded him only as a means to exert diplomatic pressure on the Bulgarians.

The Rus' prince conquers the core regions of the Bulgarian state in 967–969, seizes the Bulgarian tsar Boris II, and rules the country through him.

Sviatoslav intends to continue his drive south against Byzantium itself, which in turn regards the establishment of a new and powerful Russo-Bulgarian state in the Balkans with great concern.

After stopping a Rus' advance through Thrace at Arcadiopolis in 970, in 971 the Byzantine emperor John I Tzimiskes leads an army north into Bulgaria and captured Preslav, the capital.

After a three-month siege of the fortress of Dorostolon, Sviatoslav agrees to terms with the Byzantines and withdraws from Bulgaria.

Tzimiskes formally annexes Eastern Bulgaria to the Byzantine Empire.

However, in effect most of the country in the central and western Balkans remains outside imperial control; this will lead to the revival of the Bulgarian state in these regions under the Cometopuli dynasty.

While Sviatoslav's campaign brings no tangible results for the Rus', it weakens the Bulgarian statehood and leaves it vulnerable to the attacks of Basil the Bulgar-Slayer four decades later.