The rapid expansion of modern molecular imaging methods since the time of their initial conception in the 1970s has given rise to numerous discoveries of molecular mechanisms that underlie brain function in health and disease. Uses in clinical diagnosis and therapy monitoring are still evolving. Future clinical trials, in which molecular imaging is imbedded and correlated with clinical outcomes, will be critical to advancing new uses for patient management. Receptor occupancy studies are already well integrated into many drug development studies and clinical trials; such studies will provide a basis for new studies that will further advance clinical uses of brain molecular imaging.