AbstractGrain boundary engineering is based on the fact that special grain boundaries (i.e. low Σ CSL) may have beneficial physical and chemical properties. It is now possible to increase and characterize the fraction of low Σ 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.