We should therefore attempt to develop industrial processes using CO₂ as a feedstock and H₂O as an electron donor in order to build a sustainable society in the near future. If H₂O does function as the electron donor, then it is important to obtain a stoichiometric ratio between the amount of O₂ evolved and the amount of CO2 reduced. Moreover, the reduction of H⁺, released from H₂O molecules, usually competes with CO₂ reduction when several heterogeneous materials are used as photocatalysts for the reduction of CO₂ with H₂O. Generally, the production of H₂ via the reduction of H⁺ is the dominant pathway. Therefore, to achieve high selectivity in the photocatalytic conversion of CO₂ with H₂O, the electrons generated through the oxidation of H₂O must be controlled to selectively. These days, we found that Ag/ZnGa₂O₄/Ga₂O₃, Ag/La₂Ti₂O₇, Ag/SrO/Ta₂O₅, Ag/ZnGa₂O₄, and Ag/ZnTa₂O₆ exhibit good conversion of CO₂ and high selectivity toward CO evolution for the photocatalytic conversion of CO2 by H2O as an electron donor.