Nickel-base alloys, as designed for gas turbine use, have reached an interesting new level of technology. Where previously the main thrust of effort had been to improve mechanical capability, the problems of alloy phase stability and hot corrosion now control much alloy development, principally because of the need for increased alloy life and because gas turbines are being used in a wide variety of ambients. Fundamental and applied studies of hot corrosion phenomena are beginning to allow understanding and progress towards solution of the problem. Sodium sulfate has been the key reactant in the case of nickel alloys. Chromium, as an alloying element, helps inhibit hot corrosion, while molybdenum and aluminum appear to be a problem.