We have to face the fact that our climate is under a lot of stress and is polluted in many different ways. Since it affects not only our every day life but also our economy and politics, the development of energy efficient technologies is a major concern of today's innovation. In order to demonstrate how significant the pollution is in some areas it is sufficient to mention that in the European Union the building stock is responsible for 77% of all the emissions. Therefore, there is a great potential of reducing greenhouse gas emissions by improving construction solutions and renovation technologies in the buildings sector. This book is a comparative study of two European coutries, Sweden and Hungary, and its aim is to give a general overview of policies, emphasize and discuss the problems, and show directions how the process of the implementation of energy efficient measures could be improved.