The control of indoor environment and the use of energy using high efficiency strategies, when appropriately considered and developed, may represent an important tool for the protection and conservation of the cultural heritage. Apart from reducing the energy consumption of primary resources/energy this principle concept/idea, in many instances makes possible the successful integration of technological solutions and the improvement of the conditions of conservation and comprehension of the palimpsests. The interaction of energy efficiency and cultural heritage is illustrated using relevant case studies. These complex subject matters, generally pertaining to different specialised fields, have until today, contributed to the building of a barrier between professionals active in the field. The book, originally conceived as a REHVA Guidebook, will attempt to find a solution to overcome this difference, particularly by considering energy efficiency as the proper tool to be used in the conservation of cultural heritage.