This is the protocol for a review and there is no abstract. The objectives are as follows: 1. To examine the effectiveness of psychological therapies in preventing PTSD and the negative emotional, behavioural or mental health outcomes in children and adolescents who have undergone a traumatic event. 2. To examine the effectiveness of psychological therapies in reducing PTSD and, the negative emotional, behavioural and mental health outcomes associated with PTSD, in children and adolescents who have been diagnosed with post-traumatic stress disorder (PTSD).