Water and wastewater treatment involves the use of one or more physical, chemical and biological processes or their combination for removing solids and organic matter from the wastewater. Advanced oxidation processes (AOPs) are a set of chemical treatment procedures designed for effectively removing organic pollutants from water and wastewater by the process of oxidation. This emerging chemical technology is based on the in-situ generation of hydroxyl radicals, which are used as strong oxidants that can be used to oxidize a wide range of chemical compounds. In some AOPs, sulphate radicals, ozone, catalyst, or ultraviolet irradiation is also used to achieve more efficient treatment. AOP is beneficial for cleaning biologically toxic or non-degradable materials such as aromatics, pesticides, petroleum constituents, and volatile organic compounds dissolved in the wastewater. A major advantage of using AOPs for wastewater treatment is that these processes do not introduce any new hazardous substances into the water since the complete reduction product of hydroxyl radicals is water. One drawback of AOPs that limit its large-scale application and industrial usage relates to high costs. This book unravels the recent studies on water and wastewater treatment using the advanced oxidation process. Researchers and students in this field will be greatly assisted by it.