A derebey (Turkish: valley lord) was a feudal lord in Anatolia and the Pontic areas of Lazistan and Acara in the 18th century, with considerable independence from the central government of the Ottoman Empire.
Derebeys were required to provide military assistance in time of war, but ruled and administered their own territories, in full freedom in practical terms, and often forming local dynasties. Their emergence were often sparked by the gradual abandon of the timar system administered by the military fiefdom of sipahis, and the tendency of the central government to sub-contract tax revenues as of the 18th century, receiving a determined sum from the derebey and outsourcing on them the task of collecting from the taxpayers themselves. In official terminology, these intermediaries were often to as âyân, although other terms were also used for describing this class whose official status, effective powers and the geographical extent of authority could greatly vary from one derebey to another, and could also evolve differently over time. The particular characteristics of their region of authority, such as economic development or its becoming an issue within contexts of international politics, also greatly influenced derebeys' destinies. While the derebeys did not seek to overthrow the Ottoman state, they did seek autonomy from the empire for themselves and their heirs. Through their collection and control of tax revenues in their region as well as only providing armed men for the sultan's wars when it benefitted their interests, the derebeys demonstrated a lack of centralized authority in the Ottoman state during the 18th and early 19th centuries.
The Russo-Turkish War of 1768-1774 saw an increase in the power and influence of the derebeys, due to the reliance of the Ottoman government on their assistance. By the end of the 18th century, during the reign of Sultan Selim III, most of Anatolia was ruled by derebeys, and their role in Ottoman affairs was prominent. Selim's successor, Mahmud II (who followed the year-long reign of Mustafa IV), oversaw the decline of the derebeys as Ottoman government became increasingly centralised and administration was conducted by appointed governors. In the 19th century, the term came to be applied to the powerful hereditary land-owners of southern and eastern Turkey. By 1866 the remaining derebeys were subjugated by a military expedition in the Çukurova region.
The derebeys gradually Ottomanized, i.e. became part in the mechanics of the central government, with the re-strengthening of the Ottoman central power in the 19th century. Many members of derebey families left lasting works serving general welfare, while others were also involved in bitter struggles that gave rise to public revolts, such as that of Atçalı Kel Mehmet Efe.