SUMMARY
This research paper aims to discuss the nature of change in the functional purpose of some archaeological and historical buildings in Cairo during the 19th and 20th centuries along with a comparative study of some of the most important heritage constructions and evidences in the world, such as the British Museum in London, as well as the Historical Railway Station of Orsay in Paris. There are some practical attempts and technical procedures that have been carried out to achieve some functional purposes, differ from the original purposes of the archaeological and historical buildings in Cairo in particular. In a similar way, this has been applied to historical and heritage buildings around the world in general. The methodology of this study will be addressed through analytical and comparative study of the original idea or the original functional purpose of these archaeological and historical buildings.The outlines and features of change in the functional purpose of these archaeological and historical buildings are represented in some technical procedures like the technique of adaptive rehabilitation or rehabilitation in terms of adaptation, so there is a necessity for conformity and harmony between heritage buildings and modern functional purpose, and this should be done without any disagreement and repulsion with the original functional purpose. There is also a necessity to protect the original functional purpose, which should be adapted to the modern functional purpose in order to achieve compatibility between old and new integration processes.