Opsins are animal photoreceptor proteins that use retinal as their chromophore (ligand) and are classified into several groups based on sequence similarity. Opn5 forms one phylogenetically separate opsin group and includes three vertebrate-specific subgroups, Opn5m, Opn5L1 and Opn5L2. In this article, we introduce highly diversified functionalities of vertebrate Opn5. Three Opn5 subgroups show characteristic spectral sensitivity, preference for retinal isomers and photoreaction process, and work as bistable photoreceptor, retinal chemoreceptor or unidirectional photoreceptor. Such broad spectrum of functionalities may be attributed to optimization for respective physiological functions.