A loss-free, thermal energy storage technology attracts a rising interest over the past years. The thermochemical energy storage is seen as a promising technology for a loss-free thermal energy store with high storage density. This paper presents the state of the art in the field of material research, process design and process development as well as the technological challenges of the thermochemical energy storage. Exemplarily two system concepts, one for low temperature applications and one for high temperature applications, are shown to demonstrate the technical capabilities of the thermochemical energy storage.