Arsenic contamination in groundwater is a critical environmental and public health issue, affecting millions of people worldwide. Its occurrence is closely linked to complex biogeochemical processes that control arsenic mobilization, transformation, and accumulation in natural systems. In particular, redox conditions, geological settings, and microbial activity play key roles in governing the distribution of arsenite [As(III)] and arsenate [As(V)] in groundwater and hydrothermal environments. This presentation provides an integrated perspective on arsenic cycling, combining field observations from Taiwan’s geothermal and groundwater systems with mechanistic insights into microbial-mediated redox transformations. Case studies highlight the strong relationship between environmental arsenic exposure and human health risks, emphasizing the urgency of effective mitigation strategies. To address this challenge, we further explore sustainable remediation approaches that couple microbial processes with engineered materials. Biologically induced mineralization and iron-based nanomaterials demonstrate high efficiency in arsenic removal and stabilization. Overall, this work presents a multidisciplinary framework linking environmental geochemistry, microbiology, and green material technologies, offering practical and scalable solutions for arsenic-contaminated groundwater.