A study of the administrative institutions of The Caliphate.The most important topics are: 1- The vizierate : beginnings: developments; Theory 2- The Diwans: a- central diwans: beginnings and developments (under the Rightly guided Cailphs, Umayyads and Abbasids) b- Defining the Diwans and their sections like the diwans of Kharaj, Jund, Post, Expenditure Bait al Mal Rasail.etc . 3- Other administrative institutions a- The Judiciary and its diwan b- The Hisba and al-Mahutasib . 1- The administration of provinces, and its diwans: a – The Amir, Amil , Chief of police; The post master. etc. b- Provencal diwans .