The correct design of the building envelope, including an informed choice of materials and their thermal properties, is a key requisite to conjugate energy efficiency, the durability of the envelope, and the indoor microclimate. Firstly, this process involves a strategic selection of building materials based on their thermal properties and performance. Designers should then adopt a multi-scale approach, both evaluating the thermal performance of individual envelope components and optimizing their overall energy efficiency. This activity should be assisted by reliable software tools that are also able to simulate advanced envelope solutions and must be complemented by effective and original evaluation methods to identify the best performing solution. In situ and laboratory measurements are recommended if possible since they can significantly improve the accuracy of the analysis. The following reprint presents advanced research and methodologies regarding the above-mentioned topics, ranging from the thermal performance of the building envelope to the energy optimization of buildings and the integration of renewable energies in the building envelope.