Cathodic protection (CP) is an electrochemical means of corrosion control widely used in the marine environment. This article discusses the two types of CP systems, namely, impressed current systems and sacrificial anode (passive) systems. It describes the anode materials used in these systems and CP criteria. The article also discusses the design considerations and procedures involved in the CP of marine pipelines, offshore structures, and ship hulls. It also illustrates the sacrificial anode calculation.