This chapter reviews some of the known neurophysiological/neuropharmacological principles underlying nucleus accumbens neuronal excitability. It presents new findings that begin to directly measure the cellular activity of rat nucleus accumbens neurons, in vivo, during spontaneous and operant guided behaviors. Basal forebrain circuitry is well recognized to be composed of numerous functional components involved in numerous aspects of integrated behaviors. The ventral striatal component of this circuitry, including the nucleus accumbens, is part of an interconnected series of forebrain and brainstem effector systems underlying goal-directed motor components of species specific behaviors. The electrophysiological data generally support the recent observations of divergent accumbens efferents depending whether their origin is from the accumbens shell or core. Due in part to the focus of the actions of psychostimulant drugs on the nucleus accumbens and the subsequent elicitation of well-described behaviors, most of the progress regarding the neuropharmacology of nucleus accumbens neurons and drugs of abuse has focused on dopamine antagonist mechanisms.