Nickel-base superalloys are used extensively in modern gas turbine engines and are subjected to a broad range of environmental conditions. At ambient and moderately elevated temperatures improved fatigue resistance can be obtained through refinement of grain size. Thermomechanical working, for example, microduplex processing, offers a means to achieve very fine grain sizes and exceptional fatigue strengths. At high temperatures grain boundaries are a source of weakness. Significant improvements in fatigue resistance can be achieved by the elimination of transverse grain boundaries. High-strain fatigue studies show that deformation occurs by coarse planar slip. Recent developments have enabled a combination of γ and oxide dispersion strengthening to be achieved. This opens possibilities for improved fatigue resistance by promoting slip dispersal. Fatigue resistance is influenced also by environmental factors. The present trend in alloy development is to provide materials having high inherent oxidation and sulfidation resistance.