Ion exchange is an essential process in wastewater treatment, widely used to remove harmful ions and pollutants from water. It works through different types of ion exchangers and mechanisms that help target specific contaminants, including heavy metals, nitrogen, phosphorus, and organic pollutants. Ion exchange plays a key role in tertiary wastewater treatment, significantly improving water quality and reducing toxic substances. As environmental challenges continue to grow, ion exchange technology offers a sustainable and cost-effective solution for various industries, such as pharmaceuticals, textiles, and chemicals. Recent innovations in resin development, such as hybrid resins and metal-oxide-based exchangers, have made the process more efficient and selective. Additionally, the reuse of spent ion exchange resins to remove emerging contaminants like per- and polyfluoroalkyl substances enhances the economic viability of this technology. This chapter highlights the importance of ion exchange in meeting regulatory standards and its growing potential in wastewater management.