This talk will discuss the relationships between subcritical crack growth and the nature of the loading, the environment under which the loading takes place and the type of material tested, and how this data is used in predictive analysis. Loading conditions will include sustained loading as well as constant and variable amplitude cyclic loading. The environments will include vacuum as a baseline environment and both gaseous and liquid aggressive environments. The comparison between crack growth behavior in brittle and ductile materials will also be made. The data will be discussed from the viewpoint of reproducibility and reliability for use in predictive analysis.