This article looks at the application of complexity theory to risk assessment in child protection practice, and how it may help to give a better understanding of risk in relation to protecting vulnerable children. Within the last 20 years increasing use has been made of the term complexity within the natural sciences. In recent times, some of the key concepts in complexity theory have started to filter through to the social sciences. The article offers an explanation of some of the key concepts in complexity theory and discusses the development of a model of assessing risk in child protection cases. (Contains 4 tables and 2 figures.)