This chapter provides an overview of post-traumatic stress disorder (PTSD)-related psychophysiological research. Specific foci include psychophysiological reactivity to trauma-related stimuli and loud tones, conditioned fear acquisition and extinction, fear memory reconsolidation blockade, and the potential usefulness of psychophysiological measures in predicting PTSD development, maintenance, and treatment efficacy. A detailed discussion is provided on the contribution of reduced parasympathetic tone and increased sympathetic activity to the heightened psychophysiological reactivity associated with PTSD. Reduced parasympathetic tone may increase the risk of cardiovascular disease. Recent technological advances in physiological recording are also described.