These Guidance Notes define the best practices and design recommendations for a ship??s corrosion protection using cathodic protection (CP) systems and provide guidelines for ship CP design@ installation@ and maintenance. Protective coatings are the most efficient way to protect ship steel structures from corrosion. However@ cathodic protection@ often in conjunction with protective coatings@ is also used to protect immersed parts of bare steel surfaces (including coating damaged areas) from corrosion. This includes the external hull surface and the internal surfaces of tanks@ such as ballast tanks. It is a common practice for a ship to have cathodic protection systems installed during its new construction. External underwater surfaces include the underwater hull and all attachments and openings such as shafts@ rudder@ stabilizers@ propeller@ propeller bracket@ sea chests@ water intakes (up to the first valve)@ and scoops thruster). The internal surfaces of various tanks include those of ballast water tanks@ fresh water tanks@ fuel storage tanks@ crude oil tanks@ bilges@ etc. Pipes@ such as condensers and heat exchangers@ should also be protected cathodically. Cathodic protection (CP) can be Impressed Current Cathodic Protection@ Galvanic Anode Cathodic Protection or a combination of both. Cathodic protection controls corrosion by supplying direct current to the immersed surface of the structure@ thus making the structure a cathode of a cell. The external hull of a ship is exposed to different waters with differing chemistries@ which have a profound influence on the current distribution from the cathodic protection system. Thus@ these Guidance Notes cover ships?? cathodic protection only.