The present paper is a review of the use of psychophysiology in diagnosis and treatment of simple phobias. The paper begins with a definition and characterization of phobic fears, together with a description of prevalence rates, age onset, and gender differences. Acquisition is then discussed within a Three-Systems model. Psychophysiological measures are described, and the typical response patterns obtained in phobic reactions are outlined. Special attention is devoted to the paradoxical response seen in blood injury phobias, and the use of beta-blockers and other pharmacological drugs. The paper is ended with a discussion of Lang’s emotional imagery as a psychophysiological model for fear reactions and fear therapy.