Intercalation by atoms (Cs, K, Ba, Pt, Si, C,...) of a monolayer graphite film deposited on a metal (Ir, Re,...) is reviewed. Atoms with low ionization potential (Cs, K, Ba,...) form a monolayer film of the intercalate under the graphite layer, whereas atoms with high unionization potential (Pt, Si, C,...) form a thick multilayer film. The high intercalation efficiency can be accounted for by weak bonding (physisorption) of the graphite film to the metal. An intercalation mechanism is proposed. The superefficient diffusion of intercalated atoms into metals is discussed.