This article describes the two principal methods, namely, metal-loss tools and casing current measurement for detecting well casing corrosion along with their limitations and advantages. It discusses factors considered in designing well casing cathodic protection systems. The factors include determination of cathodic protection current by casing polarization test and CPP test or by mathematical models; calculation of casing-to-anode separation; isolation of the casing from other facilities; consideration of stray current interference from other dc power sources; and determination of the size and the location of the anode bed for effective current output for the desired life of the anode bed. The article concludes with a discussion on commissioning and monitoring of cathodic protection systems.