Cathodic protection is the electrical solution to the corrosion problem. In this article, the history of cathodic protection (CP) is traced, and the design fundamentals are developed, including the three components of a corrosion system, the three elements of an electric circuit, and the three configurations causing potential difference. CP is the process of forcing a metal to be more negative (cathodic) than the natural state. Corrosion of metal equipment in contact with the earth is a natural phenomenon. To control this corrosion, CP systems intentionally sacrifice one material to protect another. For this system to work, there must be a complete electric path from a negative source, to the protected structure, through the electrolyte, via the ground bed, to the positive side of the source. Some more methods are also handled to control corrosion that is discussed.