This book reviews the building renovation process by systematizing the phases of analysis and prior knowledge through a project that not only considers energy savings but also thoroughly examines complex issues, such as defining the correct new functions and answers to new needs. The urgency of climate change and the many problems associated with the excessive use of energy are forcing a reorganization of the renovation process with an interest in reusing existing buildings with a more sustainable approach. The adaptive transformation of old buildings has become a dominant theme in many urban renewal projects. It must necessarily include strategies for energy efficiency, reduced pollutant emissions, improved environmental performance, economic sustainability and cultural identity. The examples selected are intended to provide evidence of good practices in the review and transformation of old buildings.