The scientific pursuit of the determination of mechanisms of corrosion of metals and alloys operating at high temperatures in thermal power generating environments has resulted in volumes of reported data, yet little achievement has been made so far. In reviewing the literature, it has been attempted here to indicate the diversified nature of the problems and the characteristics of various parameters such as mineralogical constituents of the fuel, fuel ash and various products of combustion (e.g. sulphurous oxides, sulphates, pyrosulphates, sulphides, etc.) in monitoring the rate of reactions, and hence corrosion, of component materials. Rapid and intensive corrosion attack due to conjoint action of gaseous, chemical and liquid phases under normal boiler operating conditions have been expressed to offer a really challenging situation for further studies.