Ijtihad (from the root jhd — the same root as jihad, meaning strenuous effort) is the exercise of independent legal reasoning to derive new legal rulings from the Islamic sources. Ijtihad is the highest form of legal activity — only a fully qualified mujtahid (one who practices ijtihad) can produce binding legal opinions. The criteria for mujtahid status are demanding: mastery of Quran, Sunnah, Arabic language, usul al-fiqh (legal theory), and more. The classical debate about the ‘closing of the gate of ijtihad’ — the argument that by ~900 AD all necessary legal questions had been answered and subsequent scholars should only follow (taqlid) established schools — is disputed in modern Islamic thought. Reformers from ibn Taymiyya to Muhammad Abduh to contemporary modernists argue the gate was never closed and ijtihad is urgently needed to address modern questions (banking, bioethics, human rights) that medieval jurists could not have anticipated.