Thermochemical energy storage (TCES) technology has the advantages of high-storage density and long-storage duration without dissipation, thus offering a promising alternative to other thermal energy storage methods. This chapter first introduces the principle and potential of TCES. TCES materials are then categorized according to working pairs and their respective advantages and disadvantages are discussed. Despite the advantages of TCES, it is still in the early stage of research and development. The key technological challenges of TCES materials are their low-thermal conductivity and agglomeration during thermochemical cycling. Various studies on addressing these shortcomings are reviewed.