Environmental pollutants threaten the health of humans and disrupt the balance of ecosystems. Their accumulation in water bodies and deposition into the food chain can result in long-term environmental degradation, chronic health disorders, and hormonal imbalance. Consequently, the early detection and continuous monitoring of these contaminants are essential, not only to safeguard public health but also to ensure the sustainability of our environment. Among the various sensing materials, rare earth-doped metal oxides have become an extremely promoting class because of their prominent physicochemical properties, surface activity, and tunable electronic structures. This chapter explores the role of rare earth-doped metal oxides, including metal oxides ZnO, Fe3O4, SnO2, SiO2, CuO, TiO2, and NiO, in the detection of an extensive array of environmental pollutants such as pesticides, heavy metals, antibiotics, toxic dyes, microplastics, and industrial effluents. Doping these metal oxides with rare earth elements like Ce, Eu, La, or Tb significantly improves their sensitivity and selectivity by modulating charge transport, extending optical absorption, and creating active surface sites. The chapter provides insights into the synthesis approaches, structural modifications, and morphological tuning that influence the sensing performance of these materials. Various detection platforms, optical, magnetic, electrical, and catalytic responses, are discussed in a generalized context to emphasize the versatility of these nanostructured oxides. Furthermore, the potential of rare earth-doped metal oxides for use in miniaturized, portable, and field-deployable sensing devices was also highlighted.