This chapter discusses thermochemical energy storage materials with a focus on materials based on adsorption and absorption (sorption). First, the principle of the sorption-based thermochemical energy storage and the criteria for the materials’ selection are outlined. Various sorption materials, working pairs, charging and discharging temperatures and energy densities are then summarised and compared. This is followed by an introduction to the characterisation of the sorption-based thermochemical materials and the sorption enthalpy calculation. Since the sorption-based materials have a very low-thermal conductivity, combined with the deliquescence, swelling and agglomeration after several thermal cycles, composite materials are introduced to address these issues. Last, an outlook into the future research into sorption-based thermal storage materials is given.