Several types of nanostructured materials have been reported with potential use in environmental applications. Depending on their physical properties, they can be used as novel biodegradable materials, environmental sensors, adsorbents (i.e., membranes and other porous structures), materials to reduce energy consumption, materials for storage or production of energy (light emitting diodes (LEDs), photovoltaic (PV) cells), and catalysts for advanced oxidation methods (AOMs) or “green” processing technologies. Semiconducting metal oxide nanomaterials such as TiO2, ZnO, CeO2, CuO, Fe2O3, Fe3O4, among others, have found specific environmental applications due mainly to their photocatalytic (PC) activity. Also, Fe3O4 and Fe2O3, supported or not, are of interest due to their capability to form highly oxidant species in solution such as Fe(IV) or to adsorb heavy metals (Cu2+, Cr6+,Ni2+, Pb2+, Cd2+, Hg2+) and other toxic ions such as As5+ and As3+. However, other metal oxides such as SnO2 and PbO2 have been used for long as electrode materials for the electrochemical oxidation of persistent pollutant molecules in wastewater. The chemical and physical properties of these materials can be tailored by carefully controlling or selecting the preparation methods as well as the precursors and synthetic conditions. In this chapter, we discuss development and use of selected nanostructured metal oxides (TiO2, ZnO, CeO2, Fe3O4, Fe2O3, doped and undoped TiO2 nanoparticles and nanotubes) that have been found to possess excellent properties for environmental remediation, in particular their application for ensuring proper water and wastewater quality through pathogenic microorganism disinfection.