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 eighteenth 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.

"Sick man of Europe" is a label given to a state located in Europe experiencing economic difficulties, social unrest or impoverishment. Although it is most famously used to refer to the Ottoman Empire whilst they were in a state of decline.