The Vilayets (Turkish pronunciation: [vilaːˈjet]) of the Ottoman Empire were the first-order administrative division, or provinces, of the later empire, introduced in 1864 with the promulgation of the "Vilayet Law", (Turkish: Teşkil-i Vilayet Nizamnamesi), as part of the administrative reforms that were being enacted throughout the empire. The term vilayet is derived from the Arabic word 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 nahiye. 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.
Labelled Map 
Vilayets of the Ottoman Empire circa 1885:
- Adana Vilayet (Adana)
- Aegean Archipelago Vilayet (Cezayir-i Bahr-i Sefid [Akdeniz Adaları])
- Aleppo Vilayet (Haleb [Halep])
- Ankara Vilayet (Ankara) (also called Angora)
- Aydin Vilayet (Aydın)
- Baghdad Vilayet (Bağdad [Bağdat])
- Basra Vilayet (Basra)
- Beirut Vilayet (Beyrut)
- Bitlis Vilayet (Bitlis)
- Bosnia Vilayet (Bosna)
- Crete Vilayet (Girit)
- Danube Vilayet (Tuna)
- Diyarbekir Vilayet (Diyarbekır [Diyarbakır])
- Edirne Vilayet (Edirne) (Also called Adrianople)
- Erzurum Vilayet (Erzurum)
- Hejaz Vilayet (Hicaz)
- Herzegovina Vilayet (Hersek)
- Hudavendigar Vilayet (Hüdavendigar) (Also called Bursa)
- Istanbul Vilayet (İstanbul) (Also called Constantinople)
- Janina Vilayet (Yanya)
- Kastamonu Vilayet (Kastamonu)
- Konya Vilayet (Konya)
- Kosovo Vilayet (Kosova)
- Mamuret-el-Aziz Vilayet (Mamuret-ül Aziz [Mamuretülaziz]) (also called Kharput, now Elazığ)
- Monastir Vilayet (Manastır)
- Mosul Vilayet (Musul) (from 1879)
- Salonica Vilayet (Selanik)
- Shkodër Vilayet (İşkodra)
- Sivas Vilayet (Sivas)
- Syria Vilayet (Şam) (Also called Damascus)
- Tripolitania Vilayet (Trablusu-Garb [Trablusgarp])
- Van Vilayet (Van)
- Yemen Vilayet (San'a)
Vassals and autonomies 
- Eastern Rumelia (Rumeli-i Şarkî): autonomous vilajet (1878 - 1885); annexed by Bulgaria in 1885
- Sanjak of Benghazi (Bingazi Sancağı): autonomous sanjak. Formerly in the vilayet of Tripoli, but after 1875 dependent directly on the ministry of the interior at Constantinople.
- Sanjak of Biga (Biga Sancağı) (also called Kale-i Sultaniye) (autonomous sanjak, not a vilayet)
- Sanjak of Çatalca (Çatalca Sancağı) (autonomous sanjak, not a vilayet)
- Cyprus (Kıbrıs) (island with special status) (Kıbrıs Adası)
- Khedivate of Egypt (Mısır) (autonomous khedivate, not a vilayet) (Mısır Hidivliği)
- Sanjak of Izmit (İzmid Sancağı) (autonomous sanjak, not a vilayet)
- Mutasarrifyya/Sanjak of Jerusalem (Kudüs-i Şerif Mutasarrıflığı): independent and directly linked to the Minister of the Interior in view of its importance to the three major monotheistic religions.
- Sharifate of Mecca (Mekke Şerifliği) (autonomous sharifate, not a vilayet)
- Mount Lebanon Mutasarrifate (Cebel-i Lübnan Mutasarrıflığı): sanjak or mutessariflik, dependent directly on the Porte.
- Principality of Samos (Sisam Beyliği) (island with special status)
- Tunis Eyalet (Tunus Eyaleti) (autonomous eyalet, ruled by hereditary beys)
Vilayets and independent sanjaks in 1917 
Vilayets and independent sanjaks in 1917:
Encyclopædia Britannica on the late Ottoman administration 
For administrative purposes the immediate possessions of the sultan are divided into vilayets (provinces), which are again subdivided into sanjaks or mutessarifliks (arrondissements), these into kazas (cantons), and the kazas into nahies (parishes or communes). A vali or governor-general, nominated by the sultan, stands at the head of the vilayet, and on him are directly dependent the kaimakams, mutassarifs, deftardars and other administrators of the minor divisions. All these officials unite in their own persons the judicial and executive functions, under the " Law of the Vilayets," which made its appearance in 1861, and purported, and was really intended by its framers, to confer on the provinces a large measure of self-government, in which both Mussulmans and non-Mussulmans should take part. It really, however, had the effect of centralizing the whole power of the country more absolutely than ever in the sultan's hands, since the Valis were wholly in his undisputed power, while the ex officio official members of the local councils secured a perpetual Mussulman majority.
- Turkish public administration: from tradition to the modern age at Google Books By Hamit Palabiyik
- Haifa in the late Ottoman period, 1864-1914: a Muslim town in transition at Google Books by Maḥmūd Yazbak
- Governing property, making the modern state: law, administration and ... at Google Books By Martha Mundy, Richard Saumarez Smith
- Chisholm, Hugh, ed. (1911). "Bengazi". Encyclopædia Britannica (11th ed.). Cambridge University Press.
- Palestine; A Modern History (1978) by Adulwahab Al Kayyali. Page 1
- A handbook of Asia Minor Published 1919 by Naval staff, Intelligence dept. in London. Page 226
- Chisholm, Hugh, ed. (1911). "Turkey". Encyclopædia Britannica (11th ed.). Cambridge University Press.
See also