Photolyases belong to the cryptochrome/photolyase protein family (CPF) which perform different functions such as DNA repair, circadian photoreceptor, and transcriptional regulation. Photolyase is a flavoprotein that repairs UV-induced DNA damages of cyclobutane pyrimidine dimer (CPD) and pyrimidine-pyrimidone (6-4) photoproducts using blue-light as an energy source. This enzyme has two chromophores: flavin adenine dinucleotide (FAD) as a cofactor and a photoantenna such as methenyltetrahydrofolate (MTHF). The FAD is essential for catalysis of the DNA repair. The second chromophore absorbs photons from the blue light spectrum and transfers energy to FAD to increase the repair efficiency of the enzyme. Phylogenetic analysis in which amino acid sequences of several hundreds of CPF members are used suggests that they form more classes than we have considered so far. In this chapter, we discussed structure-functions and reaction mechanisms of different classes of photolyases.