Sultan (; Arabic: سلطان sulṭān, pronounced [sʊlˈtˤɑːn, solˈtˤɑːn]) is a position with several historical meanings. Originally, it was an Arabic abstract noun meaning "strength", "authority", "rulership", derived from the verbal noun سلطة sulṭah, meaning "authority" or "power". Later, it came to be used as the title of certain rulers who claimed almost full sovereignty (i.e., not having dependence on any higher ruler) without claiming the overall caliphate, or to refer to a powerful governor of a province within the caliphate. The adjectival form of the word is "sultanic", and the state and territories ruled by a sultan, as well as his office, are referred to as a sultanate (سلطنة salṭanah).

The term is distinct from king (ملك malik), though both refer to a sovereign ruler. The use of "sultan" is restricted to Muslim countries, where the title carries religious significance, contrasting the more secular king, which is used in both Muslim and non-Muslim countries.

Brunei and Oman are the only independent countries which retain the title "sultan" for their monarchs. In recent years, the title has been gradually replaced by "king" by contemporary hereditary rulers who wish to emphasize their secular authority under the rule of law. A notable example is Morocco, whose monarch changed his title from sultan to king in 1957.