A muḥtasib (Arabic: محتسب, from the root حسبة ḥisbah, or "accountability") was "a holder of the office of al-hisbah in classical Islamic administrations", according to Oxford Islamic Studies. Also called ‘amil al-suq or sahib al-suq, the muḥtasib was a supervisor of bazaars and trade, the inspector of public places and behavior in towns in the medieval Islamic countries, appointed by the sultan, imam, or other political authority. His duty was to ensure that public business was conducted in accordance with the law of sharia.

Hisbah, the office and root of muḥtasib, is an Islamic doctrine referring to "enjoining good and forbidding wrong" of shariah law, and "by extension, to the maintenance of public law and order and supervising market transactions". But whether muḥtasibs devoted themselves to hisbah frequently or vigorously in every region of the Muslim world, or focused instead on the orderly function of the marketplace, regulating weights, money, prices (though sometimes collecting bribes), is disputed.

According to Sami Hamarneh, in "religious terminology", hisbah "denotes providing for ... for oneself, or seeking reward in life to come for a good deed." It acquired another meaning sometime early in the 9th century" as "a religious position or bureau the aim of which was to carry out" enjoining good and forbidding evil.

At least one scholar (Willem Floor) distinguishes the muḥtasib, officials who in Islamic law are following "fard 'ayniyya [political duty]" and mutatawwi ("true believers" or volunteers who follow fard kifaya [individual duty] of Islamic law to take "the initiative to see to the upholding of the requirements of the law and the hisbah".

Another related definition of Hisbah is not as an official function with any special connection to marketplaces, weights and measures, etc.; but as a "personal" duty of Muslims enjoined in Quranic verses such as 3:110 and 9:71, to right wrongs "committed by fellow believers, as and when one encountered them." It was "mainly an invention" of Al-Ghazali" (d.1111). Al-Ghazali also used the term muhtasib, but to refer to "the one who performs hisba" -- a forbidder of wrong in general and not specifically a functionary overseeing marketplaces -- leading to some confusion, according to historian Michael Cook.

A large "scholastic heritage" on the subject of who was to do the forbidding, what was to be forbidden, and whom was to be told there actions were forbidden, was developed by Al-Ghazali and other medieval scholars.

While most of the literature describing of the function of muhtasib that scholars use comes from two sources: the "theoretical writings on the role, function, and tasks of the muhtasib", and from "practical manuals to guide the muhtasib in his work in a particular place and time".

One of the earliest and most influential manuals for a muḥtasib is the Nihāyat al-rutba fī ṭalab al-ḥisba by Abd al-Rahman ibn Nasr ibn Abdallah al-Shayzari (d. 1193). Another example of book on hisbah (by a famous scholar (Ibn Taymiyya) translated as Public Duties in Islam the institution of the Hisba) that as one review put it, not only "delineates the duties of the Muhtasib" but preaches that it "is not just the commercial behavior of the Muslims that needs to be regulated, but also their behavior to God", and that fraud in business transactions is not wrong because it "was "judged 'immoral,' but because such behavior stemmed from a distorted notion of the deity and, therefore, violated the basic tenets of Islam".