Real time high temperature corrosion monitoring is a subject that has caused much controversy in the academic world. Some did not believe it was possible using electrochemical instrumentation. Others felt it should be feasible but found the results were not reliable. This paper examines the development route of practical real-time high temperature corrosion rate determination considers how the technology is consistent with traditional electrochemical theory and reviews recent applications that demonstrate is use to characterize aggressive environments and fouling behavior in large combustion plants.