Films produced on titanium depend on the nature and concentration of electrolyte, forming voltage, current density, and temperature. In most cases, dense films of limited thickness are produced, but in some cases, thick, porous films result. Physical, chemical, and electrical nature of the coatings are discussed together with their relation to the substrate surface character. Evidence indicates that films prepared in aqueous electrolytes are not a pure rutile structure. These coatings are highly uniform, insulating, and adherent.