In this chapter the current state of concepts in selective oxidation reactions is discussed by examining the functions of supported active sites in a redox catalyst of the VxOy type. As model reactions the conversion of propane into its olefin propene and into its oxidation product acrylic acid are considered. The discussion is based on a set of chemical equations giving the minimum of molecular transformations in correct stoichiometric relations for the atoms and formal charges needed to achieve the desired reaction.