This chapter describes the repertoire of electrocommunication behaviors and the generalized anatomy and connections of the electro-sensory-motor system of weakly electric gymnotiforms. Electroreceptive organisms can detect electrical stimuli passively or actively. The duration of the Electric organ discharges waveform is controlled by the kinetics of the electrocytes’ ionic currents. The association, synapse type, degree of electrotonic coupling, relative size and organization, and ratio between pacemaker and relay neurons vary among gymnotiform genera. Electric fishes can be subdivided on the basis of voltage output into strongly and weakly electric fishes. Active electroreception is less common; it involves organisms emitting an electric field that interacts with the surrounding environment and then detecting the distortions that the environment causes to this electric field. Steroid hormones have been shown to exert slower, long-term changes to the electrical properties of the neurons in the premotor areas and the pacemaker nucleus.