Aluminide coatings have been widely used in the aircraft industries for the protection of gas turbine engine hot section components against oxidation and/or hot corrosion. This paper considers modes of coating degradation under conditions of cyclic oxidation, hot corrosion and corrosion erosion interactions during service as well as the effects of interdiffusion between coating and substrate alloys either during service or coating application. It also discusses means of improving existing coatings as well as advanced coating systems currently under development. In assessing coating performance, consideration must be given to the influence coatings may have on substrate properties such as mechanical strength, resistance to creep and resistance to mechanical and thermal fatigue. Finally it is stressed that proven performance for a given coating/substrate combination is no guarantee that no deleterious reaction will occur, when the same coating is used with a different substrate alloy. Therefore, coating substitution requires re qualification.