It has been long realized that much, if not most, engineering use of metals at elevated temperature involves periodic changes in temperature or stress or both. However, the engineer has available for most metals only constant stress and temperature data for design purposes. This poses the question of how changes in stress or temperature modify the constant stress and temperature behavior of metals and thus the designs based on such behavior. It was decided by the Gas Turbine and General Research Panels of the Joint ASTM-ASME Committee on the Effect of Temperature on the Properties of Metals to hold a Symposium on the Effect of Cyclic Heating and Stressing on Metals at Elevated Temperatures. The Symposium is intended to cover those situations involving relatively slow changes in stress or temperature, or both. In practice many such changes are aperiodic, and much of the experimental work covering this Symposium uses periodic variations. It is hoped that certain general considerations may, however, be deduced from the experimental results herein. As far as cyclic variation of stress is concerned, extremely rapid stress variation is commonly considered under the general subject of fatigue. This subject is not encompassed in order to limit the scope of the Symposium. The dividing line between what might be called a periodic variation of stress and a rapid variation of stress leading to a fatigue failure is obviously hard to define. However, it is apparent that both differences in experimental technique and in application to design problems have led to such a division being easily made.