This book provides an overview of changes in legislation in Australia concerning both family law and child protection law. The topic is important as the Australian Government has identified that the rate of mental disorder in some cohorts of children is high and rising. These cohorts of children live in families where they are vulnerable because they are exposed to risk factors that can be changed by a coordinated effort from parents, therapists, and lawyers.  The aim of the book is to identify psycho-legal concepts that need to be understood by professionals who work in the fields of child custody and child protection, and to bring these concepts together to improve coordination between the two fields of practice. The purpose of the book is to be a practice manual for professionals from the disciplines of law, social work, and psychologists who work in specialized legal roles dealing with families where children are vulnerable to developing mental health difficulties.    Volume 4 of the book provides a perspective from a mental health clinician about concepts and principles that arise in Australian family-oriented courts, and that need to be shared between disciplines. This book proposes that some concepts be identified as psycho-legal as the concepts need to be shared between disciplines who work with court-involved families. The book also proposes that psycho-legal concepts be shared between the jurisdictions of child custody and child protection. In this book, proposals are made to improve collaboration between disciplines and to maximize the best interests of children.