Ijmaʿ (الإجماع) is a term in Islamic legal theory (uṣūl al-fiqh) referring to the consensus of qualified scholars (mujtahidun) on a point of religious law. Alongside the Qur'an, the Sunna, and analogical reasoning (qiyas), ijma is traditionally counted among the four primary sources of Islamic jurisprudence in Sunni legal theory, though its precise definition, scope, and binding force are subjects of substantial disagreement among jurists and schools. Definitions vary as to whose agreement counts (all Muslims, all scholars, scholars of a particular era or region), what subject matter it covers, and how such agreement is identified and verified; these contested points are addressed further at ijma-definition-debate and related pages.

Classical jurists developed several competing accounts of ijma. Some held that only the consensus of the companions of Muhammad (ṣaḥaba) carries full authority, while others extended the concept to the consensus of jurists in any generation. A further distinction is drawn between explicit consensus (ijma sarih), in which scholars openly state agreement, and tacit consensus (ijma sukuti), inferred from the absence of recorded dissent. Jurists have also disputed whether ijma, once established, is reversible by later generations, and whether it can address matters not already governed by clear scriptural text. The Zahiri school, associated with jurists such as Ibn Hazm, restricted recognized ijma to the consensus of the companions alone, rejecting broader or later claims of scholarly consensus as a valid independent source of law - a position discussed at ijma-zahiri-viewpoint.

Modern scholarship, including both reformist Muslim thought and Western academic studies of Islamic law, has further debated whether claims of ijma in classical legal texts reflect genuine, verifiable agreement or retrospective rhetorical claims used to settle disputed questions. This has implications for debates over the use of ijma as a vehicle for legal change in the present day, discussed further at ijma-history.

• Majority Sunni view: Ijma, once properly established among qualified scholars, constitutes a binding and infallible source of law, ranking immediately after the Qur'an and Sunna. See ijma-binding-authority-viewpoint.
• Zahiri view: Only the consensus of the companions of the Prophet constitutes valid ijma; later scholarly consensus is not an independent source of law. See ijma-zahiri-viewpoint.
• Shia views: Twelver Shia legal theory generally treats ijma as derivatively authoritative only insofar as it discloses or approximates the position of an infallible imam, rather than as an independent source of law in its own right. See ijma-shia-viewpoint.
• Reformist/modernist view: Historical claims of ijma are often overstated or constructed after the fact, and the mechanism should be reconceived - for instance as the consensus of elected legislative bodies or representative institutions - to permit legal adaptation to modern conditions. See ijma-modernist-reform-viewpoint.
• Skeptical/revisionist academic view: Some Western and Muslim historians of law argue that documented instances of genuine, verifiable scholarly consensus are rare, and that “ijma” functions in practice more as a retrospective label for positions that became uncontested over time than as a real-time deliberative process. See ijma-revisionist-viewpoint.

• The application of ijma to scientific and cosmological questions - notably claims that a historical consensus among Muslim scholars endorsed a geocentric cosmology - has become a point of dispute in discussions of Islam and astronomy. See heliocentrism-islamic-astronomy-ijma-controversy.

• ijma-history
• ijma-definition-debate
• ijma-binding-authority-viewpoint
• ijma-zahiri-viewpoint
• ijma-shia-viewpoint
• ijma-modernist-reform-viewpoint
• ijma-revisionist-viewpoint
• Heliocentrism - Islamic Astronomy Viewpoint
• heliocentrism-islamic-astronomy-ijma-controversy
• Usul Al Fiqh

• Wael B. Hallaq, A History of Islamic Legal Theories: An Introduction to Sunni Uṣūl al-Fiqh (Cambridge: Cambridge University Press, 1997).
• Bernard G. Weiss, The Spirit of Islamic Law (Athens, GA: University of Georgia Press, 1998).
• Ahmad Hasan, The Doctrine of Ijma' in Islam: A Study of the Juridical Principle of Consensus (Islamabad: Islamic Research Institute, 1976).
• Camilla Adang, Muslim Writers on Judaism and the Hebrew Bible: From Ibn Rabban to Ibn Hazm (Leiden: E.J. Brill, 1996).
• George Makdisi, “The Significance of the Sunni Schools of Law in Islamic Religious History,” International Journal of Middle East Studies 10, no. 1 (1979): 1-8.