In this chapter I look at the challenge facing child psychotherapists who take on the role of expert witness in family law cases, assessing parenting capacity when there is concern about serious harm to the child. Health expert witness teams are to be set up in NHS Trusts throughout England over the next few years to provide evidence to family courts and child psychotherapists could have a central role in this work (Chief Medical Of®cer 2006). I will argue that although the court is an unfamiliar setting, it can provide a thinking space and the containment necessary to protect the best interests of the child. As child psychotherapists, our psychoanalytic thinking and observations of children and families are valued by the judiciary, helping to elucidate the complex dynamics of family life. We can offer a view of the children's experience of the world and how it is communicated through their behaviour and play. I will show how some families can use this enforced space for re¯ection to explore their parenting dif®- culties, and renew their bond with their child. Others desperately hold on to denial, and project blame on to others, even at the cost of permanent separation from their child. This will be evident as I describe my involvement as a child psychotherapist in a specialist psychotherapeutic assessment service, the Cassel: from outpatient interviews, through a residential assessment to a recommendation for court. The assessment is a dynamic process in which the parents' capacity to change to meet their children's needs is tried and tested in a therapeutic setting.