The oxidation of ClO2 by OCl- is first order with respect to both reactants in the neutral to alkaline pH range: -d[ClO2]/dt = 2k(OCl)[ClO2][OCl-]. The rate constant (T = 298 K, mu = 1.0 M NaClO4) and activation parameters are k(OCl) = 0.91 +/- 0.02 M-1 s(-1), DeltaH(double dagger) = 66.5 +/- 0.9 kJ/mol, and DeltaS(double dagger) = -22.3 +/- 2.9 J/(mol K). In alkaline solution, pH > 9, the primary products of the reaction are the chlorite and chlorate ions and consumption of the hypochlorite ion is not observed. The hypochlorite ion is consumed in increasing amounts, and the production of the chlorite ion ceases when the pH is decreased. The stoichiometry is kinetically controlled, and the reactants/products ratios are determined by the relative rates of the production and consumption of the chlorite ion in the ClO2/OCl- and HOCl/ClO2-reactions, respectively.