A method is presented for predicting the conditions under which graphite will react with cesium at high temperatures and low cesium pressures to form compounds. The method is based on the available thermodynamic data on cesium-graphite compounds and on an understanding of the nature of the bonding forces in these compounds. An expression is given for the threshold pressure, at any temperature, below which no reaction will occur between cesium and graphite. The structural deterioration and swelling of graphite which occurs when cesium-graphite compounds are formed can be avoided by keeping the cesium pressure below the threshold value. The information on the compatibility of cesium and graphite is of potential use in the design of MHD direct-conversion systems, in high-temperature graphite reactors and in systems that require the availability of cesium vapor at controlled pressures, such as thermionic converters.