Reduction of SO2 by CO to elemental sulfur on fluorite oxide and transition metal/fluorite oxide composite catalysts is discussed within the redox framework. The oxygen vacancies on the fluorite oxide are active catalyst sites and their creation is a key step to initiate the redox reaction. Transition metal/fluorite oxide composites demonstrate a strong synergism for the reaction, A reduction kinetics study of the copper/ceria system as a model composite catalyst has found that surface oxygen is highly active but its activity is inhibited by SO2 adsorption. The TPR profile of the copper/ceria catalyst shows a significantly lower reduction peak than the individual components.