Electrodes based on films of conducting material have been making increasingly important contributions to electrochemical experiments in recent years, and the possibilities for future growth and novel applications are outstanding. The use of films as electrodes makes possible numerous experiments that would be difficult or impractical to implement with conventional bulk electrodes. Discussion here emphasizes either “thin” (< 5 µm thick; usually quite a bit thinner) or “thick” (> 5 µm usually quite a bit thicker) film electrode materials, consisting of a conductor, either a continuous film or spatially patterned, most commonly deposited on a suitably prepared insulating substrate. Films consisting primarily of insulators are not considered here, except to the extent that they may be used to form patterned arrays or electrodes with special geometries. For example, films used to form chemically modified electrodes are discussed in Chapter 13.