Dedicated as it is to the in-depth rehabilitation of urban heritage in the Islamic world, the Historic Cities Programme (HCP) of the Aga Khan Trust for Culture deals with a complex reality. For historic cities harbour an important architectural legacy that goes well beyond the realm of “bricks and mortar”. Their monuments and their traditional urban patterns speak to us about the attitudes, the aspirations and the living conditions of past generations of human beings. That is how cities gain their symbolic dimension and how they are enabled to dispense cultural identity. While the architectural shell, due to its material inertia, tends to resist the effects of time, the more volatile social realm is subject to changes and transformations that are not immediately reflected in the built form containing it. It is this delayed interaction between physical structures and more intangible social, emotional and spiritual factors that makes interventions in historic cities particularly challenging, because once the delay leads to structural incongruence, remedial action is needed.