Anodic protection or the prevention of corrosion by impressed anodic current, is a very recent innovation, and its development has been based entirely on electrode-kinetics principles. To illustrate the principles of anodic protection, consider the system illustrated in fig.10-17. An active-passive metal M is corroding in the active state at a rate equal to icorroion. In this particular system, only the active state is stable and the metal cannot spontaneously transform to the passive condition without application of an external current.