The article reviews the biogeochemical redox processes and their impact on contaminant dynamics. Redox processes, driven by electron transfer, are crucial for understanding environmental health and can inform engineered remediation strategies. These processes control the formation and dissolution of mineral phases, influencing the release or sequestration of inorganic contaminants. Key elements such as Fe, Mn, C, P, N, S, Cr, Cu, Co, As, Sb, Se, Hg, Tc, and U are affected by redox cycling, which impacts their chemical speciation, bioavailability, toxicity, and mobility. Redox-active humic substances and mineral surfaces can catalyze the transformation and degradation of organic contaminants. The article highlights recent advances in understanding these processes and their implications for contaminant fate and transport, while also identifying future research needs, including the development of new instrumentation, the elucidation of electron transfer mechanisms, and the modeling of complex biogeochemical environments.The article reviews the biogeochemical redox processes and their impact on contaminant dynamics. Redox processes, driven by electron transfer, are crucial for understanding environmental health and can inform engineered remediation strategies. These processes control the formation and dissolution of mineral phases, influencing the release or sequestration of inorganic contaminants. Key elements such as Fe, Mn, C, P, N, S, Cr, Cu, Co, As, Sb, Se, Hg, Tc, and U are affected by redox cycling, which impacts their chemical speciation, bioavailability, toxicity, and mobility. Redox-active humic substances and mineral surfaces can catalyze the transformation and degradation of organic contaminants. The article highlights recent advances in understanding these processes and their implications for contaminant fate and transport, while also identifying future research needs, including the development of new instrumentation, the elucidation of electron transfer mechanisms, and the modeling of complex biogeochemical environments.