The construction sector makes a fundamental contribution to climate protection efforts. In Germany, energy-saving construction activities have been enhanced for several decades now, with many of them setting examples for European countries. For many decades now, Hans Erhorn of the Fraunhofer Institute for Building Physics has played a major role in defining the standards of energy saving construction in Germany and Europe. It is in close collaboration with him as a Principal Adviser that Fraunhofer IBP addresses the overall energy performance of buildings and issues relating to the energy transition in city districts.