Of all the signals collected and analyzed during psychophysiological detection of deception or polygraph testing, the electrodermal response (EDR) is the most robust and informative. Research shows that the EDR is easily collected and is simple to measure and interpret. However, despite this there are many misconceptions of the EDR with the polygraph profession. This paper was written as a reference on EDR for both the practicing and student polygraph examiner. It describes the present state of the scientific knowledge of the EDRs, and provides a description of the use of EDRS in the science of Psycho-physiological Deception Detection (PDD) testing. The paper concludes with how to apply the EDR to deception detection. Tables, figures, and references