This academic study by Mansour Khamis Mansour Raslan delves into the significant role of *Ijma'* (scholarly consensus) as a foundational principle in Islamic jurisprudence and theology. It specifically examines how *Ijma'* has been employed as a valid form of argumentation within the *Usul al-Din* (principles of religion), addressing core theological and creedal issues. The research meticulously analyzes doctrinal consensuses (*Ijma'at Aqadiya*) that emerged and were applied up to the end of the fourth Hijri century. Raslan provides a critical historical survey, exploring the methodology, scope, and impact of *Ijma'* on the formation of early Islamic theological thought. This work offers invaluable insights for scholars and students interested in Islamic intellectual history, *Usul al-Din*, and the evolution of doctrinal authority.