[en] It is generally believed that many properties of solid interfaces are ultimately determined by their structure and composition at the atomic level. We report here on work in two areas of grain boundary (GB) research in which structure-property correlations have been investigated recently. HREM observations in connection with computer modeling of GBs in fcc metals have given considerable insight into correlations between GB energy and atomic-scale GB structure. Efforts to understand and possibly control the supercurrent transport behavior across GBs in high-temperature superconductors require the combination of microstructure characterizations with investigations of electric transport properties. In both areas considerable progress is being made and has already lead to important insights concerning interfacial properties