This document summarizes different types of potentiometric electrodes used to measure ion activity. It discusses electrodes of the first kind like silver/silver chloride electrodes and electrodes of the second kind like calomel electrodes. Redox electrodes and the hydrogen electrode are also covered. The document explains how to write the Nernst equation for different half-cells and full electrode systems. It provides examples of liquid junction cells and discusses sources of potential and factors that affect potentiometric measurements.