Grain boundary engineering is based on the fact that special grain boundaries (i.e. low SIGMA CSL) may have beneficial physical and chemical properties. It is now possible to increase and characterize the fraction of low SIGMA interfaces in polycrystalline materials, thereby improving their bulk properties by controlling the material and processing parameters. The successful application of grain boundary engineering to the problem of intergranular degradation of a nickel-base alloy is described. The potential beneficial application of grain boundary engineering to ordered intermetallic compounds, electrical properties, nanocrystalline materials, orientation textures and materials for nuclear waste storage is discussed.