Since their appearance in the first land plants, genes encoding class III peroxidases have been duplicated many times during evolution and now compose a large multigene family. The reason for these many genes is elusive, and we are still searching for the specific function of every member of the family. Nevertheless, our current understanding implicates peroxidases as key players during the whole life cycle of a plant, and particularly in cell wall modifications, in roles that can be antagonistic depending on the developmental stage. This diversity of functions derives in part from two possible catalytic cycles of peroxidases involving the consumption or release of H₂O₂ and reactive oxygen species (e.g. O₂⁻, H₂O₂, OH).