Research on the basal ganglia suggests that they are critically involved in building up sequences of behavior into meaningful, goal-directed repertoires. Work on rodents, monkeys and humans suggests that the basal ganglia act as part of a distributed forebrain system that helps to encode such repertoires through behavioral learning, and that is engaged in the expression of such repertoires once they have been internalized. The basal ganglia also may be critical to the expression of innate behavioral routines. Experimental findings on reward-based learning suggest that neural activity in the striatum and substantia nigra, pars compacta changes during behavioral learning. New evidence also suggests extreme specificity in the neural connections interrelating the basal ganglia, cerebral cortex and thalamus. Adaptive control of behavior may centrally depend on these circuits and the evaluator-reinforcement circuits that modulate them.