Abstract: Thermochemical energy storage (TCES) is a preferred approach for long duration thermal energy storage due to its high energy storage density and low heat loss. The reactants used in gas-solid and gas-gas medium and high temperature TCES systems were summarized, the characteristics of various thermochemical storage materials were reviewed, and the research challenges including reactant modification, development of novel materials, and catalyst optimization were discussed in depth. The performances of fixed bed, moving bed, and fluidized bed thermochemical reactors were comparatively analyzed, and suitable reactor types were proposed for different reaction systems. Open and closed thermochemical reaction systems were comprehensively analyzed, with their performance under variable operating conditions and the advantages and disadvantages in practical applications evaluated. An economic analysis of TCES systems was conducted to assess their commercialization potential, and the costs at different technology readiness levels were estimated.