Perhaps the most popular definition of psychology is the science of mind and behavior. However, the interrelation between mind and behavior is one of continuing controversy. The present paper examines this enduring issue from the perspectives of George J. Romanes, an early comparative psychologist, Edwin G. Boring, an influential experimental psychologist, and Howard Rachlin, an estimable recent behaviorist. Their respective positions shed considerable light on both the theory and practice of behavioral psychology.