The booklet provides insights into the main results and findings of the four year European funded EFFESUS project. Organised in five main chapters, the booklet contains a wide range of information to support communities in improving energy efficiency in European historic districts. It includes key project outcomes of EFFESUS such as strategies for energy assessment, the analysis of existing solutions, the development of innovative solutions and a software-based Decision Support System, as well as presenting non-technical barriers encountered and experiences of the case studies.