High temperature (, ) water has been found to greatly accelerate fatigue crack growth rates in carbon and low-alloy steels. Current ASME Code fatigue design curves are based entirely on data obtained in air. While a factor of 2 on life was applied to the air data to account for environmental effects, the actual effects have been found to be an order of magnitude greater in the low-cycle regime. A great deal of work has been carried out on these environmental effects by talented investigators worldwide. The ASME Code Subgroup on Fatigue Strength has been working for on the development of new fatigue design methods and curves to account for high temperature water environmental effects. This paper presents an overview of the data and analyses used to formulate proposed new environmental fatigue design curves, which maintain the same safety margins as existing Code fatigue design curves for air environments, and a historical summary of ASME Code Work in this field.