Advanced oxidation processes (AOPs) are promising techniques that can be used for various environmental applications. Currently, AOPs are receiving extensive interest from many researchers mainly due to their non-selective behaviour, their potential for pollutant oxidation, and the lack of solid waste formation in the majority of them. However, there are some knowledge gaps in the scientific literature, such as the efficiency and applicability of AOPs for real environmental water and/or wastewater matrices, the effectiveness of AOPs for toxicity reduction, the influence of environmental conditions and constituents on AOPs, cost of studied treatment methods, etc. This reprint presents original research papers and reviews focused on various environmental applications of AOPs, including comprehensive reviews on specific AOP technologies, focusing on their applications in specific sectors, such as industrial, agricultural, and municipal wastewater. A dedicated chapter is focused on the application of AOPs for toxicity reduction. The application of AOPs for the removal of organic pollutants such as Contaminants of Emerging Concern, pesticides, or dyes from water matrices of diverse origin is featured in the present reprint as specific chapters. Also, two chapters are dedicated to the innovative application of AOPs in the field of greenhouse gas reduction.