Water purification processes often involve chlorine-based disinfectants which consequently leads to formation of chloro oxyanions (ClOx−), potent water-soluble oxidizing agents. These chlorine species are kinetically stable in water which allows them to persist and buildup to hazardous concentrations. Chlorite (ClO2−), a common contaminant in water purification processes, has been labeled as a top ten major water contaminant by the United States Environmental Protection Agency. Therefore, there is pressing interest in developing methods for removal of ClOx− species from water. Chlorite dismutases are heme b dependent enzymes that catalyze the unimolecular decomposition of ClO2− into chloride (Cl−) and molecular oxygen (O2) with remarkable efficiency. Catalytic O−O bond formation is a rare process in Nature as the only other well characterized example occurs in photosystems II. Clds are great candidates for bioremediation purposes and an excellent model for investigating catalytic O−O bond formation as the catalyzed reaction is not hindered by the need to pump protons. The goal of this work is to gain mechanistic insight into catalytic ClO2− decomposition by Cld and to investigate the structural features that tune the reaction pathway for productive O2 evolution. Cld from Klebsiella pneumoniae and Dechloromonas aromatica are the representatives used in this work. Since heme is the cofactor in these enzymes, a variety of spectroscopic tools have been utilized to probe the electrostatic landscape of the active site. Vibrational (resonance Raman and infrared), optical absorbance, and electron paramagnetic resonance spectroscopies were used to characterize the heme environment. Various ligand complexes were prepared to probe non-reactionary states of the enzymes while reactionary states were directly observed through use of stopped-flow spectrophotometry and freeze-quenched methods. Site directed mutagenesis studies of key amino acids were performed in combination with the above techniques to elucidate how changes in the electronics of the heme pocket alter catalytic activity. These studies have allowed for development of a proposed mechanism that describes the sequential steps and identification of the reactive intermediates leading to catalytic O2 production that accounts for the pH dependency of the reaction that was previously not understood.