[en] The advantages of high resolution electron diffraction and imaging have been revealed in a wide variety of metallic systems, providing insight into the mechanisms of such phase transformations as ordering, spinodal decomposition, grain boundary precipitation, and the martensitic reaction. Structural discontinuities in interphase interfaces (atomic plane ledges) and grain boundaries (plane matching defects) have been identified with high precision, and compositional variations on an atomic scale have been detected, including solute segregation within approximately 10 A of a grain boundary. In the study of ceramics, primary effort has been directed toward the detection of thin intergranular films with notable success. Atomic dimension microledges have also been revealed in crystallization interfaces, polytype boundaries and transformation fronts, and compositional variations near grain boundaries have recently been recorded in lattice images of a Magnesium Sialon. It therefore appears that the technique holds equal promise for analysis of the fundamental mechanisms of crystallization, phase transformation, diffusion and solute segregation in ceramics as well as metallic alloy systems. The work presented here represents some of the potential of high resolution methods and is an initial step towards complete atomic characterization of materials. The most desirable progression of such research should lead to the attainment of structural images similar to those that are currently being used to explore the atomic arrangements in mineralogical specimens. This requires only a slight improvement in the contrast transfer characteristics of present day electron optics