This book reports the literature survey of the corrosion inhibition of iron in different media. and the use of rare earth metals as green corrosion inhibitors for iron in clear and polluted sodium chloride solutions. Several electrochemical techniques were used, such as potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and the recent one electrochemical frequency modulation (EFM). The surface of iron specimens were examined using scanning electron microscope (SEM) and Energy disperse X-ray (EDX) techniques. The adsorption isotherm was determined. The effect of temperature was studied in order to determine whether the adsorption of rare earth metals on iron surface was physically or chemically and to determine some thermodynamic parameters such as energy of activation, enthalpy of activation and entropy of activation. The different tecniques used gave good agreement.