This chapter provides a brief overview of nanomaterials, including classification, shape and structure, nanomaterial types, and applications in the degradation of recalcitrant organic contaminants. With the rapid advancement of nanotechnology science, the use of nanomaterials in environmental applications, particularly water treatment, has piqued the scientific community’s interest in recent decades. Nanomaterials have unique properties such as surface-to-volume ratio, quantum effect, low band-gap energy, and so on, which enhance catalytic performance. Wastewater treatment is a critical task of the twenty-first century since it protects the health of our environment and living beings. Because of its ability to affect both living and nonliving organisms, wastewater is always viewed as a serious source of environmental contamination. Many physical, biological, and chemical modes of treatment are implied to comply with wastewater discharge standards set by competent national agencies for environmental protection.