This chapter summarizes the development of the global principles of historic building reuse and the theories of fundamental intervention, starting from the end of the eighteenth century down to the related principles’ integration into comprehensive sustainable development agendas at the beginning of this century. The chapter raised some research questions and presented three historic churches from the Syrian coast that need reuse and activation. Then, it attempted to answer the questions through a literature review and a case study of international examples of the adaptive reuse of historic churches from America and Europe in an assortment of functions. The presented case studies focused on the abandoned historic churches’ original structure and materials and incorporating them into the design for the new usage, era needs and techniques, where their conservation and adaptive reuse emphasize the aging of original surfaces, walls and other components as a form of respect for the place’s memory in some cases, as well as using the creative design in other cases to provide the needs of the new functions. The chapter concluded with some guidelines and essential points to be considered in the process of historic building/church’ adaptive reuse in Syria and worldwide.