Results that characterize the fatigue crack propagation and ductile fracture characteristics of two steam turbine shaft materials are presented. Comparison of the usual mechanical properties and the results of chemical analyses indicate these materials are typical of the class of steel alloys often used in steam turbines. A range of environmental considerations are addressed, including laboratory ambient conditions and high-temperature saturated steam conditions. Fatigue crack growth results suggest that, for the environment considered, these shaft materials do not exhibit a strong environmental dependence of properties. Further limited data suggest that overloads typical of turbine applications do not significantly alter crack growth rate behavior. Fracture data, including Charpy V-notch (CVN), KIc, and JIc, indicate these materials exhibit ductile fracture over the range of temperatures encountered in service. Fracture morphology in all cases suggests the action of a ductile mechanism, either ductile rupture for fracture or striation forming for fatigue crack growth. Application of these results in the context of turbine fracture control planning illustrates the utility of fracture mechanics concepts. Its limitations are discussed with reference to situations in which corrosion fatigue pitting is responsible for crack initiation.