Ann M. Graybiel, of the Massachusetts Institute of Technology, Okihide Hikosaka, of the National Institutes for Health’s National Eye Institute, and Wolfram Schultz, of the University of Cambridge, have been pioneers in the study of the structure, organization and functions of the basal ganglia, a group of nuclei (clusters of neurons) located deep within the forebrain. Their groundbreaking work has fundamentally transformed our understanding of the basal ganglia and has led to influential new ideas about how the brain learns and retains new habits and skills, manages movements and processes rewards for learning and decision-making. It has also deepened our understanding of a wide range of neurodegenerative and neuropsychiatric disorders in which the basal ganglia and behavioral control are compromised.