Psychologists working in Medical settings have taken place since the growth surge in the field following World War II. Clinical Psychology professional growth escalated with its empirically developed assessment and treatment interventions. The initial invitations in Medicine came to Psychologists from departments of Psychiatry. The recognition of the knowledge competencies (i.e., Brain & Behavior, Social Interactions, Learning, Memory, Perception) fundamental to the training of doctoral level Clinical Psychologists expanded to the Veteran’s Administration service and medical specialties of Neurology and Physical Medicine. The integrated knowledge and skills of the Psychologist to design, implement and interpret research investigations of patients’ behavior fortified the flourishing of Psychologists in general hospital settings.