Graphite reacts with a large number of substances to give lamellar compounds in which the reactant is present in the form of monolayers separated by one or more carbon layers. The compositions of some of the compounds can differ in the repeat frequency of the reactant layer, and occasionally also in the arrangement of atoms within the reactant layer. The “concentration stage” of a compound is defined as the ratio of the number of carbon layers to that of reactant layers. Thus a compound of Stage 1 is always the most concentrated one in a range of intercalation compounds of the same reactant. A survey of some graphite inclusion compounds is given in Table 1.