Photonic electrochemistry, taken in its most general sense, involves the intimate interaction of light with electrochemical processes. Thus, processes in which illumination of the electrode–electrolyte interface produces charge-transfer events as well as electrochemical reactions that produce light as a product (electro-chemiluminescence, ECL) fall in this category. A third related area is the electroanalytical detection of transient species formed by a photochemical process which takes place in solution. Techniques such as spectroelectrochemistry are excluded from consideration, since they utilize photons as a nonperturbing probe of purely electrochemical processes.