The field of oxidative water treatment has evolved significantly in the last decades. Initially, disinfection was the main focus, but more recently oxidation processes such as ozonation are widely applied for micropollutant abatement. Initially research and application focused on the disappearance of target compounds, however, nowadays the formation of transformation products is an important issue, because they can be detected thanks to improved analytical tools. Furthermore, the question about the toxicological relevance of transformation products for water quality has to be considered. Based on these concerns, it is obvious, that (eco)toxicological test procedures of such processes needed to be included in the overall assessment. Furthermore, the biodegradability of transformation products emerged as an important topic for the assessment of the relevance and fate of these compounds. The strong focus on the feasibility of micropollutant abatement during ozonation should not distract from the fact, that most of the oxidation power is lost to the organic matrix (dissolved organic matter, DOM). To this end, knowledge from the reactions of individual compounds can be applied to assess the reactivity of DOM with ozone and allows to potentially predict the formation of oxidation byproducts. In the future, the broad knowledge gained in the last decades should be compiled for the development of prediction models for kinetics, transformation product formation and (eco)toxicity, to improve the assessment of oxidation processes in general beyond a case by case evaluation of individual organic micropollutants.