The rule of law offers legal certainty, laying down boundaries to the state's playing field. The precautionary approach stipulates that the absence of scientific certainty is no reason not to act to prevent harm. Here, uncertainty frames action. The precautionary approach potentially expands the state's playing field, and this expansion might well undermine the precepts of the rule of law. The certainty-uncertainty axis exposes a tension between the rule of law and the precautionary approach in what Ulrich Beck has termed the world risk society in second modernity. It is this tension that is the focus of analysis in this article. © 2013 John Wiley & Sons Ltd.