a Muslim judge who renders decisions according to the Sharīʿah, the canon law of Islām. The qadi hears only religious cases such as those involving inheritance, pious bequests (waqf), marriage, and divorce, though theoretically his jurisdiction extends to both civil and criminal matters. Originally, the qadi's work was restricted to nonadministrative tasks—arbitrating disputes and rendering judgments in matters brought before him. Eventually, however, he assumed the management of pious bequests, the guardianship of property for orphans, imbeciles, and others incapable of overseeing their own interests, and the control of marriages for women without guardians. The qadi's decision in all such matters was final.

Because the qadi performed an essential function in early Muslim society, requirements for the post were carefully stipulated: he must be an adult Muslim male of good character, possessing sound knowledge of the Sharīʿah, and a free man. In the 7th and 8th centuries the qadi was expected to be capable of deriving the specific rules of law from their sources in the Qurʾān, Ḥadīth (traditions of the Prophet), and ijmāʿ (consensus of the community). This view was later modified to allow the qadi to accept as absolute the opinions of one of the four orthodox Muslim law schools.

The second caliph, Umar Iʿ, was the first to appoint a qadi to eliminate the necessity of his personally judging every dispute that arose in the community. Thereafter it was considered a religious duty for authorities to provide for the administration of justice through the appointment of qadis.