Efficient energy use is a primary objective of the energy system transformation. On the way to a sustainable energy supply, this means not only efficient renewable energy conversion but also increasing the efficiency of existing system components. The focus here is on the energy consumption in buildings, since this accounts for about 40 percent of the final energy consumption in Germany. Fraunhofer ISE develops technologies and components for efficient building envelopes and for the heating and cooling supply in buildings, including material development for heat transformation. We also focus on thermal storage and operation management and develop complete energy concepts for buildings.