An important issue in the neural control of posture and movement is how motor-related areas of the cerebral cortex modulate the activity of the output nuclei of the basal ganglia. In this chapter, the functional significance of the 'hyperdirect' cortico-subthalamo-pallidal pathway is emphasized, and further a new dynamic model of basal ganglia function is presented. When a voluntary movement is about to be initiated by cortical mechanisms, a corollary signal is conveyed through the 'hyperdirect' pathway to first inhibit large areas of the thalamus and cerebral cortex that are related to both the selected motor program and other competing programs. Next, another corollary signal is sent through the 'direct' cortico-striato-pallidal pathway to disinhibit this second pathway's targets, and ensure activation of only the selected motor program. Finally, a third corollary signal is sent through the 'indirect' cortico-striato-external pallido-subthalamo-internal pallidal pathway to strongly inhibit this third pathway's targets. This sequential information processing ensures that only the selected motor program is initiated, executed and terminated at the appropriate times, whereas other competing programs are canceled.