Technical limitations and equipment factors can alter and distort the desired physiologic waveforms. These technically derived distortions can easily be confused with findings seen with disease or injury. The electrodiagnostic (EDX) consultant must be aware of these sources of error and learn techniques to minimize them. Understanding how the electrophysiologic instrument processes and displays biologic signals will help you to avoid misinterpreting erroneously derived data from instrumentation errors. EDX instrumentation is not a “black box” but can be thought of as physical links in a chain, or functionally, like a sequence of events. This chapter acquaints one with the signal path and the nature of the components. It explains a simple but practical description of the inner workings of EDX instrumentation. They are the electrodes; the signals; the displays; and the stimulator.