Taking the Urgenda case on climate change liability as an example, this article researches the more general question into the legitimacy of risk regulation by civil courts. Which principles determine the legitimacy of a civil court’s participation, especially in the domain of societal risk regulation? The central claim is that these principles concern (amongst many other things) the position of the court, the tools of the court, and the attitude of the court. In other words, they have their source in constitutional law, civil (procedural) law, and professional ethics respectively. This claim is substantiated by an analysis of these principles, their interpretation, and the way they contribute to a normative/theoretical framework for the assessment of the legitimacy of judicial rulings.