Peroxiredoxins compose a superfamily of peroxidases ubiquitously found throughout evolution in prokaryotes, archaea and eukaryotes. These enzymes contain a conserved catalytic peroxidatic cysteine (Cp) in the N-terminal region of the protein. The residues surrounding Cp and the catalytic site appear also to be well conserved. Peroxiredoxins can be classified either into three subfamilies according to their catalytic mechanism or into five subfamilies according to sequence homology. Notably, the number of peroxiredoxin genes increased during evolution. In eukaryotes, the higher number of genes coding for peroxiredoxin family members is due to the existence of different isoforms targeted to different subcellular compartments but is probably due also to the acquisition of new functions. Indeed, it has been postulated that the antioxidant protective role of peroxiredoxins, which is particularly critical in prokaryotes, in yeasts and in parasitic eukaryotes, may have evolved to a modulatory role in hydrogen peroxide signaling in plants and animals.