A review is presented of high-temperature fatigue mechanisms, with emphasis on nickel-base superalloys. It is shown that the slip character of a material (wavy versus planar), the extent of creep in the fatigue cycle, and the degree of oxidation all influence the mode and rate of fatigue crack initiation and propagation. These concepts are then used to explain the generally observed effects of temperature, mean stress, holdtime, and frequency on high-temperature fatigue life.