The variety of clinical neurophysiological studies corresponds to a variety of structural generators in the body, including muscles, sweat glands, peripheral nerves, and various components of the central nervous system. Each structural generator may have associated with it several different types of physiological potential. This chapter reviews the generators of electrophysiological potentials in terms of basic cellular electrophysiology and the anatomical structures that generate electrophysiological potentials of clinical interest. Knowledge of the generators of the potentials recorded in clinical neurophysiological studies is helpful in understanding the characteristics and distribution of the recorded potentials and is the first step in correlating the alterations seen in disease states with the pathological changes demonstrated in the underlying generators.