This book studies the political, economic and religious aspects of the reign of the 'Abbāsid caliph, al-Qādir billāh, who assumed power in 381/991.It gives a balanced description of his achievement and reveals the causes of political and economic decline of the'Abbāsid caliphate.Instead of being a submissive caliph, al-Qādir tried to get rid of the Buwayhid tutelage and presented himself as politico-religious opposition party against the Shī'ites and Buwayhid amīrs. He rejected the appointment of the Shī'ite sharīf to the post of grand qādī who had been appointed by Bahā'al-Dawla. He led a movement of a Sunnite restoration in which he condemned Mu'tazilism and Rāfidism and all allegedly deviant doctrines. Inspired by the Hanbalites, al-Qādir wrote the epistles called the Qādirite Creed in which he acknowledged the excellence of the Sunnite orthodoxy and denounced the teachings of the Mu'tazilites, Ash'arites, and Rāfidites, in particular on the issue of Kalām (Words) of God and His attributes. In addition, to oppose the prevailing Shī'ite literature on the theory of the Shī'ite imāmate, the caliph encouraged the Sunnite scholars to compose the theory of the Sunnite caliphate.