This document discusses ion exchange, the process by which similarly charged ions can be separated using an ion exchange resin. It describes the principles of cation and anion exchange and how ions are reversibly exchanged between the solution and resin. Different types of ion exchange resins are classified based on their chemical nature and source. The document outlines factors that affect ion exchange separations and provides examples of applications such as water softening and separation of inorganic/organic/biochemical compounds.