This article considers the modernisation of family justice, set in train by the Family Justice Review and given legal force by the Children and Families Act 2014, with specific reference to public law care proceedings. It does so through the prism of Complexity Theory that has been used extensively to analyse public sector policymaking, including child protection, but that has not to date been applied to family justice. It shows how the Family Justice Review was influenced, from its terms of reference to its proposed solutions, by the rational paradigm that has dominated UK policymaking for decades. Rationalism is, it is argued, of limited value to driving policy in a system as complex as family justice and the use of a performance indicator to enforce compliance has proved to be problematic. Core concepts of Complexity are explained and an analysis of modernisation through the lens of Complexity is provided. The article concludes by setting out principles derived from Complexity to guide family justice through recovery.