Publisher Summary The chapter gives a detailed description of reference electrodes. The composition of a good reference electrode (RE) remains effectively constant, unvarying for the duration of an experiment. It provides a stable potential for controlled regulation of the working electrode (WE) potential. The reaction at the RE can be reversible. It permits a potential to be calculated from the Nernst equation, as well as have the capability to recover its potential after a current stress. Proper experimental design prevents incompatible species present in an electrolyte from reacting with the RE materials. Species that are in an electrochemical cell can interfere with the performance of an RE by poisoning the controlling redox process or increasing the solubility of the reference couple. All REs consist of four essential parts: body, top seal, junction, and active component of the electrode. Many of these elements are interchangeable and can be tailored to meet a variety of experimental conditions. The active component of an RE defines the baseline potential that can be developed by the RE.