In Chapter 2, the concept of faradaic impedance was introduced, whereby a heterogeneous electron transfer reaction can be modeled as an equivalent electrical circuit. In the simplest case, at small overpotentials, we saw how it was possible to represent the electrochemical reaction kinetics by a single resistor, since the small net current is linearly related to ŋ and is therefore said to be ohmic. Electrochemical techniques in which the current and potential fall within this linear region are referred to as small-amplitude techniques and will be discussed briefly in Chapter 5. Mathematical and experimental advantages are sometimes associated with such techniques, particularly in the study of the heterogeneous electron transfer process per se. In the present and following chapter we will consider large-amplitude controlled-potential and controlled-current techniques. These techniques operate in the nonlinear region, where current is exponentially related to overpotential. The large-amplitude techniques prove to be useful for certain analytical applications and for studies of coupled chemical reactions.