Ion exchange processes are essential for water and environmental management, providing effective methods to remove harmful ions from water and wastewater. By using ion exchange resins, target ions are selectively replaced with harmless ions from the resin's structure, resulting in water purification and improved quality. This versatile technology addresses a wide range of contaminants, including heavy metals, nitrates, radionuclides, and organic pollutants. In forensic science, ion exchange has gained recognition for its ability to analyse aqueous, soil, and biological samples, enabling the detection and identification of trace substances that are critical for investigations. This chapter explores the principles, types, mechanisms, and applications of ion exchange in forensic science, with a focus on its qualitative and quantitative analysis capabilities for water contaminants, soil samples, and other environmental matrices. It covers the detection of heavy metals from various sources, such as drug solutions (methadone, morphine, heroin), water extracts from street drugs, and postmortem tissues. Additionally, ion exchange helps detect organic pollutants and nutrients in water, soil, and air. Factors like resin choice, operational parameters, and regeneration protocols impact the system's efficiency. The integration of ion exchange with analytical techniques like spectroscopy, chromatography, and electrochemical sensors enhances environmental monitoring, forensic investigations, and regulatory compliance. Future research aims to improve ion exchange materials, making them more selective, regenerable, and effective for environmental and forensic applications while addressing current challenges and limitations.