Ijtihad (Arabic: اجتهاد ijtihād, lit. effort, physical or mental, expended in a particular activity) is an Islamic legal term referring to independent reasoning or the thorough exertion of a jurist's mental faculty in finding a solution to a legal question. It is contrasted with taqlid (imitation, conformity to legal precedent). According to classical Sunni theory, ijtihad requires expertise in the Arabic language, theology, revealed texts, and principles of jurisprudence (usul al-fiqh), and is not employed where authentic and authoritative texts (Qur'an and ahadith) are considered unambiguous with regard to the question, or where there is an existing scholarly consensus (ijma). Ijtihad is considered to be a religious duty for those qualified to perform it. An Islamic scholar who is qualified to perform ijtihad is called a mujtahid.
By the beginning of the 10th century, development of Sunni jurisprudence prompted leading Sunni jurists to state that the main legal questions had been addressed and the scope of ijtihad was gradually restricted. In the modern era, this gave rise to a perception among Western scholars and lay Muslim public that the so-called "gate of ijtihad" was closed at the start of the classical era. While recent scholarship has disproved this notion, the extent and mechanisms of legal change in the post-formative period remain a subject of debate.
Starting from the 18th century, some Muslim reformers began calling for abandonment of taqlid and emphasis on ijtihad, which they saw as a return to Islamic origins. Public debates in the Muslim world surrounding ijtihad continue to the present day. The advocacy of ijtihad has been particularly associated with Islamic modernists and purist Salafi thinkers. Among contemporary Muslims in the West there have emerged new visions of ijtihad which emphasize substantive moral values over traditional juridical methodology.