The War of Barbastro (also known as the Siege of Barbastro) is an international expedition, sanctioned by Pope Alexander II, to take the Spanish city of Barbastro from the Moors.

A large army composed of elements from all over Western Europe takes part in the successful siege of the city (1064).

The war is part of the Reconquista, but in its international and papal character it presages the Crusades of the next two centuries.