A number of procedures and devices used to monitor corrosion damage and metal loss are discussed. The advantages and drawbacks of these methods are reviewed. The factors which need to be considered in selecting a corrosion monitoring system include the purpose of the program, the cost and availability of the equipment, reliability of the system, and the nature of the corrosive stream. The problems which accompany a plant corrosion program, including safety, potential for leaks, and misleading data, are discussed. Various commercial devices employing polarization resistance, electrical resistance, polarization behavior, and alternating current (AC) are included. Problem areas in corrosion monitoring are discussed, together with needs for future development.