Behavioral inhibition is a temperament characterized in infancy and early childhood by a tendency to withdraw from novel or unfamiliar stimuli. Children exhibiting this disposition, relative to children with other dispositions, are more socially reticent, less likely to initiate interaction with peers, and more likely to develop anxiety over time. Until recently, a dominant model attributed this disposition to reductions in the threshold for engaging the circuitry supporting fear learning, particularly the amygdala. Recent work, however, also has implicated striatal circuitry and other regions that constitute components of a presumed reward system. A series of studies found that behaviorally inhibited adolescents display heightened activation of striatal structures to cues indicating an opportunity to receive reward. This article reviews evidence implicating dual roles for fear and reward circuitry in the expression of behavioral inhibition.