Abstract This first chapter aims to be an introduction to the whole of the book. It starts with a presentation of the concept of energy and its types, then referring to energy in the building sector, and providing some data on energy consumption in buildings around the world. After presenting the current regulatory environment regarding energy in buildings, a description is made of new types of materials and building envelopes as well as modern thermal facilities that allow obtaining the requirements of comfort with greater energy efficiency. In the last part of the chapter, a brief introduction to the exergy methodology and the advantages of using it in the building sector is presented, both from an energetic, economic and environmental point of view. Finally, a brief history of the use of exergy methodology and thermoeconomics in buildings is given.