When designing medical equipment, it is essential, and required by regulation, to keep patient safety in mind with regard to the potential for electric shock hazards. Regulation requires multiple means of patient protection and means of operator protection to insure safety. In this chapter, the authors become familiar with optical isolation, which allows two electrical isolated circuits to pass a signal from one to the other using light to transmit the signal while the circuits are completely electrically isolated. They implement a galvanically isolated amplifier that can be used to transmit physiological signals derived from a patient connection to a non-isolated oscilloscope and personal computer. The objectives are to: understand optocouplers and their limitations, understand galvanic isolation, and understand isolated DC to DC power supplies. On the non-isolated side, the output of the phototransistor applies current to R5/R6 which is adjusted to a nominal DC value of 6 volts.