Using density functional methods, the initial reaction steps of limonene ozonolysis have been investigated with a focus on primary ozonide formation and its decomposition to Criegee intermediates and carbonyl compounds. The ozonide formation is highly exothermic, and the decomposition channels have similar free energies of activation, Delta G*, indicating that there is no primary pathway for ozonide decomposition. Assuming that ozonide formation is the rate limiting step, the theoretical rate coefficient, k = 1.6 x 10(-16) molecule(-1) cm(3) s(-1), evaluated at the CCSD(T)/6-31G(d,p)//BHandHLYP/cc-pvdz level and 298.15 K for d-limonene is in good agreement with the experimental value, k(exp) = 3.3 x 10(-16) molecule(-1) cm(3) s(-1). The theoretical Arrhenius expression is also in good agreement with experimental results.