The kinetics of dye-sensitized oxidation reactions are considered. Utilization of rate of oxygen absorption measurements to provide information on light intensity and the quantum yield of triplet formation of the dye is discussed. The way in which solvent isotope effects, sensitizer-substrate triplet-triplet energy transfer processes, and quenching of the sensitizer excited singlet state by the substrate affect the kinetics is considered. Quantitative measurements on the quenching of the excited singlet states of Methylene Blue and Rose Bengal by anions, beta carotene, and 2.5 diphenylisobenzofuran are reported. A comprehensive rate expression is obtained for oxidation reactions in which the substrate interacts with the excited singlet and triplet states of the sensitizer, and with singlet oxygen. -- AATA