ESDU 89031 provides comprehensive guidance for the selection of surface treatments that improve the fatigue strength of steels primarily by inducing surface compressive stresses that inhibit the initiation and growth of cracks. Three main groups of treatments are covered, each itself subdivided. They are mechanical methods of cold working (shot peening, thread and fillet rolling, and pressing for holes), thermal treatments (induction, flame, laser or electron beam hardening) that induce the stresses by surface contraction on quenching from the austenitic to the martensitic state, and thermochemical treatments (carburising, carbonitriding, nitriding and ferritic nitrocarburising) that enhance the surface properties and also induce the compressive stresses through the expansion due to chemical change at the surface. Tables summarise the major advantages and limitations of each of the methods, and indicate the potential fatigue strength improvement to be expected. A separate table shows, according to component, the current treatments usually applied to a wide range of commonly-met parts, such as pistons, shafts, springs and so on. A systematic procedure for selecting a treatment appropriate to the component is illustrated by a flowchart, although it is recognised that the final decision will be influenced by cost, convenience and availability, as well as the technical issues.