Water pollution is a major global problem at present, involving inorganic and organic contaminants such as heavy metals, pesticides and pharmaceutical compounds, as well as pathogens. Therefore, the development of water-management strategies and appropriate water-treatment technologies has been the subject of intense research for decades. This chapter reviews the potential use of redox-reactive minerals as reactive media in environmental cleanup technologies especially in the removal of arsenic, nitrate, persistent organic pollutants and pathogenic microbes. The properties and applications of five classes of redox-reactive materials are summarized: zero-valent metals, mixed-valence iron oxyhydroxides, Fe-bearing clays, mixed-valence manganese oxides and titanium and zinc oxides. Examples and case studies that demonstrate the significant role of these reactive materials in water-treatment processes are also provided.