Photoelectrochemical reactions are defined as the electrochemical processes where the electronically excited states take part. Photoelectrochemical reactions are divided into two cases. The first one is the case in with the excitation of electrons in the electrode itself plays an essential role in the electron transfer process. The second one is the case where the excited species in the solution take part in the electrode process. Studies on these two fields are reviewed. The latter case with the semi-conductor electrode is particularly interesting in relation with the photographic spectral sensitization. Photoelectrochemical process with semi-conductor electrodes such as TiO₂ and ZnO can be spectrally sensitized with dyes. Emphasis is laid on the close correlation between the spectral sensitizations of photoelectrochemical process and photographic process with AgBr.