Jet engine rotors are the most highly stressed large volumes of material in the engine. They possess millions of inch pounds of kinetic energy at normal speeds. Considerable care in design and analysis must be taken to ensure that the parts do not fail over the full life cycle of the engine. In this paper, major design criteria are identified and discussed, with special emphasis on the long-life aspects of disk design methodology. The role of fracture mechanics is discussed as it applies to intrinsic material defects as well as the residual life of the part after crack initiation. Future trends, including the impact of powder metallurgy on design, and retirement of disks for cause are discussed.