In diplomatic history, the Eastern question was the issue of the political and economic instability in the Ottoman Empire from the late 18th to early 20th centuries and the subsequent strategic competition and political considerations of the European great powers in light of this. Characterized as the "sick man of Europe", the relative weakening of the empire's military strength in the second half of the nineteenth century threatened to undermine the fragile balance of power system largely shaped by the Concert of Europe. The Eastern question encompassed myriad interrelated elements: Ottoman military defeats, Ottoman institutional insolvency, the ongoing Ottoman political and economic modernization programme, the rise of ethno-religious nationalism in its provinces, and Great Power rivalries. In an attempt to triangulate between these various concerns, the historian Leslie Rogne Schumacher has proposed the following definition of the Eastern Question:

The "Eastern Question" refers to the events and the complex set of dynamics related to Europe's experience of and stake in the decline in political, military and economic power and regional significance of the Ottoman Empire from the latter half of the eighteenth century to the formation of modern Turkey in 1923.

The period in which the Eastern Question was internationally prominent is also open to interpretation. While there is no specific date on which the Eastern question began, the Russo-Turkish War of 1828–1829 brought the issue to the attention of the European powers, Russia and Britain in particular. As the dissolution of the Ottoman Empire was believed to be imminent, the European powers engaged in a power struggle to safeguard their military, strategic and commercial interests in the Ottoman domains. Imperial Russia stood to benefit from the decline of the Ottoman Empire; on the other hand, Austria-Hungary and United Kingdom deemed the preservation of the Empire to be in their best interests. The Eastern question was put to rest after the First World War, one of the outcomes of which was the collapse and division of the Ottoman holdings.

The Eastern question emerged as the power of the Ottoman Empire began to decline during the 18th century. The Ottomans were at the height of their power in 1683, when they lost the Battle of Vienna to the combined forces of the Polish–Lithuanian Commonwealth and Austria, under the command of John III Sobieski. Peace was made much later, in 1699, with the Treaty of Karlowitz, which forced the Ottoman Empire to cede many of its Central European possessions, including those portions of Hungary which it had occupied. Its westward expansion arrested, the Ottoman Empire never again posed a serious threat to Austria, which became the dominant power in its region of Europe. The Eastern question did not truly develop until the Russo-Turkish wars of the 18th century.

According to Karl Marx's writings around the Crimean War, the main factor of the Eastern question was Russian imperialism towards Turkey—with Turkey being a barrier that would protect the rest of Europe, and thus Britain's interests laid with the Ottoman Empire during the Crimean War.

The Napoleonic era (1799–1815) brought some relief to the faltering Ottoman Empire. It distracted Russia from further advances. Napoleon invaded Egypt but his army was trapped there when the British decisively defeated the French fleet at Aboukir Bay. A peace interlude in 1803 allowed the army to return to France.

To secure his own domination and to render the rest of Europe virtually powerless, Napoleon established an alliance with Russia by concluding the Treaty of Tilsit in 1807. Russia pledged to provide aid to Napoleon in his war against Britain; in turn, the Emperor of Russia would receive the Ottoman territories of Moldavia and Wallachia. If the Sultan refused to surrender these territories, France and Russia were to attack the Empire, and the Ottoman domains in Europe were to be partitioned between the two allies.

The Napoleonic scheme threatened not only the Sultan, but also Britain, Austria and Prussia, which were almost powerless in the face of such a potent alliance. The alliance naturally proved accommodating to the Austrians, who hoped that a joint Franco-Russian attack, which would probably have utterly devastated the Ottoman Empire, could be prevented by diplomacy; but if diplomatic measures failed, the Austrian minister Klemens von Metternich decided that he would support the partition of the Ottoman Empire—a solution disadvantageous to Austria, but not as dangerous as a complete Russian takeover of Southeastern Europe.