The integration of heat pumps is an effective measure to increase the energy efficiency of energy systems. The focus of the Annex 57 is on increasing flexibility through heat pumps in energy systems that are coupled with different technologies and in which end consumers act as prosumers (multi-vector energy systems). The achievable flexibility is system-serving and its services can be offered on different markets. Using international case studies, factors influencing the technical and economic potential for flexibility options will be evaluated and suitable business models derived. In this way, economically and ecologically sensible pilot projects will be identified and concepts for flexibility applications will be outlined and further developed.