This Symposium was sponsored by the Gas Turbine Panel of the ASTM-ASME Joint Committee on the Effect of Temperature on the Properties of Metals. It resulted from an increasing awareness on the part of metallurgists and designers that the atmosphere in which a high-temperature component will operate must be carefully considered before a suitable material can be selected. In many cases, the corrosive aspects of the service will far outweigh the mechanical factors, such as creep and stress-to-rupture. The work presented herein demonstrates forcibly that creep and stress-rupture data obtained in the conventional air atmosphere may be disastrously misleading. Oxidation from air is shown to be a more favorable condition than was commonly supposed. This calls for a re-evaluation of many design Criteria, and suggests that testing in atmospheres other than air should be more general than is now the case. Temperatures are going up, not only in the relatively new gas-turbine fields, but also in steam turbines, boilers, oil refining and many allied activities. Some of these industries have been relatively free of corrosion troubles for many years. However, the dependence of corrosion on temperature is well known, and it is not surprising that increases of only a few degrees in a given atmosphere have made all the difference between success and failure in some instances.