This paper applies a complexity theory approach to the idea of certainty in law. It considers how the idea of legal certainty is generally treated as being central to traditional approaches to the rule of law, and examines how autopoiesis maintains a type of legal certainty in the face of events that breach legal expectations. From here the paper reflects on how complexity theory characterises certainty – with a particular focus on the concepts of emergence, contingency, and adaptation. The tensions which these concepts introduce into an account of legal certainty are then considered through the lens of a Stacey diagram (Stacey, 1993).