Potentiometric membrane electrodes are electrochemical devices that can be used to quantify numerous ionic and nonionic species. This class of electrochemical sensors can be divided into ion-selective and gas-sensing membrane electrodes. The first half of this article mainly focuses on the subclasses, the membrane potential, electrode selectivity limitations and the methods of analysis of the ion-selective membrane electrodes. These methods of analysis include the use of calibration curves, addition techniques, subtraction techniques, and titration. The second half outlines gas sensing membrane electrodes, and discusses important elements that must be considered in addition to the potentiometric membrane electrode to ensure...