The microstructure of copper-alumina (Cu-Al2O3) composites that have been prepared via the melt infiltration of liquid copper into porous alumina preforms was studied in detail, using various transmission electron microscopy (TEM) techniques. Two different samples-with open pore diameters of 0.2 and 0.8 mum-were investigated. For both specimens, a single crystalline copper network that extended throughout the open porosity of the alumina preform was observed. An amorphous glass phase that contained silicon and calcium was observed at the Al2O3/Cu/Al2O3 triple junctions. The diameters of these amorphous pockets, which were strongly faceted along the Al2O3 grains, were up to 20 and 100 nm for the initial pore sizes of 0.2 and 0.8 mum, respectively. A glass phase that contained silicon and calcium also was present at the Cu/Al2O3 interfaces, whereas the Al2O3 boundaries remained dry, Detailed high-resolution transmission electron microscopy investigations have shown that the interfacial glass phase at the Cu/Al2O3 intel faces exhibited a uniform equilibrium film thickness along the interface region. However, the interfacial film thickness was dependent on the orientation of the Al2O3 grain, and its value varied from 0.4 nm for Al2O3 rhombohedral-plane termination (((1) over bar 012)) up to 1 nm for Al2O3 basal-plane termination ((0001)).