The Greco-Turkish War of 1897 or the Ottoman-Greek War of 1897, also called the Thirty Days' War and known in Greece as the Black '97 or the Unfortunate War, was a war fought between the Kingdom of Greece and the Ottoman Empire. Its immediate cause involved the status of the Ottoman province of Crete, whose Greek-majority population had long desired union with Greece. Despite the Ottoman victory on the field, an autonomous Cretan State under Ottoman suzerainty was established the following year, with Prince George of Greece and Denmark as its first High Commissioner.

The Kingdom of Greece was established in 1832 and was the successor state to the First Hellenic Republic. It was internationally recognised by the Treaty of Constantinople, where Greece also secured its full independence from the Ottoman Empire after nearly four centuries.