The waqf is an inalienable charitable endowment under Islamic law in which a founder permanently dedicates revenue-bearing property, such as land, shops or a bath, to fund a designated public or pious purpose in perpetuity. Formalised in the early Abbasid period, it became the principal mechanism for building and maintaining the fabric of the Islamic city, financing mosques, madrasas, hospitals, fountains, caravanserais, roads and bridges outside the state treasury. A typical foundation paired an income-generating bazaar or bathhouse with the institution it supported, binding commerce and welfare into a single endowed complex. At its height in the Ottoman Empire, waqf assets are estimated to have held roughly a third of all agricultural land and to have provided the bulk of social services.
The waqf supplied the durable, self-perpetuating finance that built and sustained the public infrastructure of Islamic cities for over a millennium, an endowment model with no clear contemporary European equal. It shaped urban form by clustering commercial and charitable buildings into endowed complexes that still define historic Muslim city centres.