Ceria plays a critical role in three-way automotive catalysis because of its oxygen-storage capacitance. More recently, these same redox properties have been shown to make ceria a good promoter for steam-reforming, water-gas-shift, and hydrocarbon-oxidation catalysis. Scientifically, ceria is also interesting because its redox properties change when it is mixed with other oxides or prepared in a nanocrystalline form. In the automotive application for example, it is necessary to mix ceria with zirconia in order to have a material with sufficient thermal stability. This talk will outline some of the key applications for ceria in catalysis. The fundamental thermodynamic properties that allow these applications will then be discussed.