The Vilayet of Aidin or Aydin also known as Vilayet of Smyrna or Izmir after its administrative centre, was a first-level administrative division (vilayet) of the Ottoman Empire in the south-west of Asia Minor, including the ancient regions of Lydia, Ionia, Caria and western Lycia. It was described by the 1911 Encyclopædia Britannica as the "richest and most productive province of Asiatic Turkey".

A vilayet, also known by various other names, was a first-order administrative division of the later Ottoman Empire. It was introduced in the Vilayet Law of 21 January 1867, part of the Tanzimat reform movement initiated by the Ottoman Reform Edict of 1856. The Danube Vilayet had been specially formed in 1864 as an experiment under the leading reformer Midhat Pasha. The Vilayet Law expanded its use, but it was not until 1884 that it was applied to all of the empire's provinces. Writing for the Encyclopaedia Britannica in 1911, Vincent Henry Penalver Caillard claimed that the reform had intended to provide the provinces with greater amounts of local self-government but in fact had the effect of centralizing more power with the sultan and local Muslims at the expense of other communities.