Controlled atmosphere electron microscopy has been used to gain a unique insight into the manner by which various additives interact with carbonaceous solids, particularly graphite. With this technique it is possible to observe directly, at the nano-scale level, changes taking place in the appearance of a solid while it is undergoing reaction with a gaseous environment at elevated temperature. Based on the studies of many metal/graphite-oxygen systems, a rationale has been presented to account for both the catalytic action of some additives and the inhibiting effect of others in the reaction. This experimental approach has also been applied to the investigation of the behavior of metal/graphite systems in both hydrogen and steam. These fundamental investigations have a direct impact on a number of industrially important areas, including indirect conversion of coal into liquid fuels, removal of carbon deposits from deactivated catalysts, corrosion of graphite electrodes and moderators in gas-cooled nuclear reactors and the oxidation protection of carbon composite structures used in aerospace applications. A review of the information gained from these studies is given along with a discussion of the interfacial phenomena associated with the different modes of catalytic action encountered in these reactions.