This short text is designed to present those aspects of the behavioral sciences that are clinically relevant to physicians in all branches of medicine. It should also be helpful to medical students studying for the behavioral sciences section of Part 1 of the national boards, to physicians taking the behavioral sciences portion of the FLEX exam, and to psychiatrists prepar­ ing for their American Board of Psychiatry certifying exam. Behavior is a product of brain function and is manifested by actions in response to sitmuli. It is fundamental to the maintenance of health, and plays a role in causing and intensifying many illnesses. Abnormal behaviors can re­ veal to us, and even allow us to localize, brain dysfunction and disease. And they can cause, for patients, their families, and friends, considerable suffer­ ing. On an intellectual level, trying to comprehend the behavior of our patients (and our own behavior as well), contributes to making medicine a truly intriguing profession.