Nanotechnology has emerged as a cutting-edge scientific field because of its ability to address various environmental issues. Nanomaterials (NMs) possess unique properties that render them useful. For example, they have a large surface area, are highly reactive, and have strong mechanical properties. These properties are highly efficient and effective for wastewater treatment. A variety of NMs, whether single or composite, have been extensively applied in wastewater treatment for the removal of organic contaminants, microbes, and heavy metals. Therefore, the purpose of the present chapter is to examine the functions of NMs in the context of wastewater treatment, highlighting their benefits. Various NMs are discussed in this chapter, including those based on carbon, metals, metal oxides, and composite NMs. Finally, prospects for future applications of NMs in the field of water remediation are emphasized.