Chemical conversion coatings provide metal surfaces with high functions. The mechanisms of film-formation of conversion coatings on the surfaces of steel, zinc-plated steel, tin-plated steel (that is, tinplate), aluminum alloy, etc. and the properties are reviewed. The following items are systematically explained: i) conventional phosphatings such as zinc, zinc-calcium and iron phosphating systems, ii) recent phosphatings such as nitrous ion- and nickel-free systems, iii) chromatings such as chemical reaction (rinse version)-and coating (no-rinse version)-systems, and iv) non-chromatings such as molybdate/phosphate-, zirconium salt- and silane-coupling agent-systems.