Groundwater contamination by arsenic and fluoride remains one of the most critical challenges for global water security, particularly in regions where these anions naturally co-occur due to shared geochemical sources and mobilization pathways. Their combined presence not only poses additional challenges for treatment strategies but also raises concerns regarding potential cumulative or synergistic health effects. In this context, adsorption-based technologies have emerged as one of the most versatile and effective approaches for the removal of both contaminants, with nanomaterials offering unique advantages derived from their high surface reactivity, tunable physicochemical properties, and adaptability to different treatment configurations. This chapter provides a comprehensive and comparative analysis of nanomaterials developed specifically for the adsorptive removal of arsenic and fluoride, highlighting the fundamental principles that govern their performance under environmentally relevant conditions. Key families of adsorbents, including iron-based nanomaterials, calcium-containing phases, and metal oxides such as Al, Mg, and Zr, are examined, together with the role of polymeric, carbonaceous, and hybrid functionalization strategies, with respect to their adsorption capacity, selectivity, operative pH windows, and behavior in chemically complex aqueous matrices. Particular attention is given to the complementary and competing adsorption behaviors exhibited by different material classes, which define both the opportunities and intrinsic limitations involved in achieving simultaneous arsenic and fluoride removal using adsorption-based materials. The chapter addresses the translation of laboratory-scale adsorption studies to natural groundwater systems, discussing key factors such as competing ions, material stability, regenerability, and challenges associated with particle recovery. Finally, emerging research directions are outlined, emphasizing the need for adsorbents capable of operating efficiently near circumneutral pH, maintaining performance in real groundwater matrices, and offering realistic pathways toward scalable, cost-effective, and sustainable adsorption-based water treatment solutions.