In general, the results of psychophysiologic research on PTSD support the presence of a variety of autonomic, sensory, and cognitive processing differences between individuals with and without the disorder. The findings are diverse and include heightened responsiveness to trauma reminders; exaggerated startle; increased conditionability and autonomic responsiveness to aversive, high-intensity stimuli; and elevated tonic or baseline physiologic activity. Increased sensitivity of the central nervous system is suggested by electrophysiologic evidence for a failure to habituate to redundant information, over-responsiveness to novel information, and reduced cortical responsiveness to overstimulation. Cognitive processing abnormalities are suggested by electrophysiologic evidence for a reduced ability to attend to task-relevant information and increased attention to task-irrelevant, trauma-related information in individuals with PTSD. Some findings, such as the heightened physiologic and P300 response amplitude responses to trauma-related stimuli and increased HR response to loud tones, have been highly replicable and appear to be as reliable as any biologic finding in the psychiatric literature. Other findings, such as increased eye-blink startle responses and tonic or baseline physiologic activity, have been less consistently replicated and have led investigators to explore how stressful or threatening experimental contexts might produce phasic alterations in the psychophysiology of individuals with PTSD. We hope that the broad range of psychophysiologic investigations and findings in PTSD will inspire others to consider possible applications of these methodologies to their own clinical and research endeavors.