The Vilayets (Turkish pronunciation: [vilaːˈjet]) of the Ottoman Empire were introduced with the promulgation of the "Vilayet Law" (Turkish: Teskil-i Vilayet Nizamnamesi) in 1864, as part of the administrative reforms that were being enacted throughout the empire. The term vilayet is derived from Arabic wilayah.

Unlike the previous eyalet system, the 1864 law established a hierarchy of administrative units: the vilayet, liva/sanjak, kaza and village council, to which the 1871 Vilayet Law added the nabiye. The 1864 law also specified the responsibilities of the governor (wāli) of the vilayet and their councils.

At the same time, the law left to the governors vast scope for independent action as well as responsibility, as part of a system intended to achieve a large degree of efficiency in ruling the provinces. The livas or sanjaks were headed by a mutasarrif, who was accountable to the wāli.

Vilayets of the Ottoman Empire in the year 1900:

Vilayets and independent sanjaks in 1917:

Vilayets of Europe in 1870