This article summarizes Urs von Gunten's 30+ year journey in the field of chemical oxidation processes for water treatment. Initially, the efficiency of chemical oxidants for micropollutant abatement was assessed based on the removal of target compounds, relying on second-order rate constants. Over time, experimental data on these constants has improved, allowing predictions for compounds without experimental data using QSAR and quantum chemical methods. However, chemical oxidation processes must be economically feasible, often limiting transformation of micropollutants and preventing complete mineralization. Transformation products (TPs) formed during oxidation are inherently present, raising questions about their biological activity, toxicity, and biodegradability. Chemical oxidants also react with water matrix components like dissolved organic matter (DOM), bromide, and iodide, often consuming most of the oxidant and forming disinfection byproducts (DBPs) that can be toxic. Despite the complexity, research has led to a good understanding of these processes, enabling optimized application in water treatment. The article discusses the kinetics, mechanisms, toxicity, and biodegradability of TPs, as well as the formation of DBPs, highlighting the role of bromide and iodide in these processes. It concludes that while chemical oxidation is complex, ongoing research continues to improve its application and control of DBPs.This article summarizes Urs von Gunten's 30+ year journey in the field of chemical oxidation processes for water treatment. Initially, the efficiency of chemical oxidants for micropollutant abatement was assessed based on the removal of target compounds, relying on second-order rate constants. Over time, experimental data on these constants has improved, allowing predictions for compounds without experimental data using QSAR and quantum chemical methods. However, chemical oxidation processes must be economically feasible, often limiting transformation of micropollutants and preventing complete mineralization. Transformation products (TPs) formed during oxidation are inherently present, raising questions about their biological activity, toxicity, and biodegradability. Chemical oxidants also react with water matrix components like dissolved organic matter (DOM), bromide, and iodide, often consuming most of the oxidant and forming disinfection byproducts (DBPs) that can be toxic. Despite the complexity, research has led to a good understanding of these processes, enabling optimized application in water treatment. The article discusses the kinetics, mechanisms, toxicity, and biodegradability of TPs, as well as the formation of DBPs, highlighting the role of bromide and iodide in these processes. It concludes that while chemical oxidation is complex, ongoing research continues to improve its application and control of DBPs.