Ion exchange resin is a kind of insoluble polymer compound with functional group (active group of ion exchange), network structure, which  is also a kind of polymer that acts as a medium for ion exchange.

Ion exchange resin provids a large surface area on and inside them, and the capture of ions is accompanied by the release of other ions, so this process is called ion exchange.

According to the difference of ion removal, ion exchange resin can be divided into cation exchange resin and anion exchange resin. As the name suggests, the resin that can remove cations is called cation exchange resin, and the resin that can remove anions is called anion exchange resin.

According to pore structure, ion exchange resins are divided into two types: gel type and macroporous type. All with physical pore structure called macroporous resin.

Ion exchange resins are widely used in separation and purification. The most common examples are water softening and water purification.