This book examines the critical turn that shaped Imami Shi’ism in the 4th and 5th centuries, especially as is seen in the works of al-Sharīf al-Murtaḍā (d. 436) of Baghdad. The intellectual context of Murtaḍā's theology is also presented against the backdrop of socio-political changes that proved beneficial to Imami Shi’its, with Murtaḍā’s status as a senior political figure positioning him to promote these changes. Combining philological and intellectual-historical approaches, Shi’i Doctrine, Mu’tazila Theology closely examines Murtaḍā’s thought accurately and clearly. It also examines the works of ʿAbd al-Jabbār (d. 415) and other researchers to measure the extent of Murtaḍā’s debt to Mu’tazila. In order to assess the authenticity and the influence of Murtaḍā’s theology whose disciples were the center of Shi’i thought till the time of Allameh al-Ḥillī (d. 726), the notes of his teacher Shaykh al-Mufīd (d. 413) and his student Shaykh al-Ṭūsī (d. 460) are also compared with his own works. Concerning the relationship between Imami scholars and political authorities, Murtaḍā’s ideologies were eventually invoked by al-Muḥaqqiq al-Karakī (d. 940) to argue for cooperation with the Safavids in Iran.