The Byzantine-Bulgarian Wars are a series of conflicts fought between the Byzantines and Bulgarians that begin when the Bulgars migrate to the Balkan peninsula in the 7th century, and successfully repulse the Byzantines while creating their own kingdom.

The Byzantines and Bulgarians continue to clash over the next century with variable success, until the Bulgarians, led by Krum, inflict a series of crushing defeats on the Byzantines.

After Krum dies in 814, his son Omurtag negotiates a thirty year peace treaty.

In 893, during the next major war, Simeon I, the Bulgarian emperor, defeats the Byzantines, while attempting to form a large Eastern European Empire, but his efforts fail.In 971 John I Tzimiskes, the Byzantine emperor, subjugates much of the Bulgarian Empire by defeating Boris II and capturing Preslav, the Bulgarian capital.

Constantinople under Basil II completely conquers Bulgaria in 1018 as a result of the 1014 Battle of Kleidon.

There are rebellions against Byzantine rule from 1040 to 1041, and in the 1070s and the 1080s, but these fail.

In 1185, however, Theodore Peter and Ivan Asen start a revolt, and the weakening Byzantine Empire, facing internal dynastic troubles of its own, is unable to prevent the revolt from being successful.After the Fourth Crusade conquers Constantinople in 1204, Kaloyan, the Bulgarian emperor, tries to establish friendly relations with the crusaders, but the newly created Latin Empire spurns any offer of alliance with the Bulgarians.

Because of his cold reception, Kaloyan allies with the Nicaeans, one of the Byzantine states created after the fall of Constantinople, instead, which reduces the crusaders' power in the area.

Even though his nephew Boril allies with the Latin Empire, Boril's successors side with the Nicaeans, despite a few continuing attacks from them.

After the Latin Empire collapses, the Byzantines, taking advantage of a Bulgarian civil war, capture portions of Thrace, but the Bulgarian emperor Theodore Svetoslav retakes these lands.

The Byzantine-Bulgarian relations will continue to fluctuate until the Ottoman Turks conquer the Bulgarian Empire in 1422 and the Byzantine Empire in 1453.