This course provides the basic concepts of cathodic protection, together with important criteria and precautions to be observed. Corrosion of metals is a result of electrochemical reactions. An electrochemical reaction is a chemical reaction accompanied by a flow of electrical current. The driving force for the corrosion of metals through electrochemical reactions is the free energy of the metal atoms in their metallic form. All chemical systems tend to change so that the free energy present is at a minimum. This is analogous to the flow of water downhill to minimize the free energy due to gravity. Most engineering metals are found in nature in a form with low free energy. These metal ores are chemical compounds consisting of the metal atoms combined with other atoms such as oxygen or sulfur. The process of breaking up these ores into their metallic and non-metallic atoms involves an addition of energy in order to free the metal atoms from the natural, low energy content chemical compounds. The corrosion process is driven by the tendency of these metal atoms to revert to their natural state. If corrosion products are analyzed, their chemical composition is usually identical to the ore from which the metal was originally obtained.