This paper describes the rationale for and development of an online cognitive-behavioural treatment for child and adolescent anxiety (BRAVE–ONLINE). It highlights the challenges involved in adapting a clinic-based intervention for delivery using the internet, with separate sessions for parents and their children (or adolescents). We outline strategies to ensure that young people remain engaged in online therapy, and describe techniques designed to optimize the alliance between clients and the online therapist. Two case studies are presented that illustrate the practical and technical aspects of implementing the intervention, and demonstrate the feasibility of achieving successful outcomes using online delivery of CBT for child and adolescent anxiety. However, firm conclusions regarding the efficacy of this approach cannot be drawn until the results of randomized controlled trials are available. The paper identifies directions for future research.