This thesis explores the roles of family and healthcare professionals in type 1 diabetes (T1D) in adolescence. The first paper is a systematic review of literature regarding family-based interventions for adolescents with T1D. Adolescence is known to be a particularly challenging time, associated with deterioration in diabetes management and increased family conflict. A systematic search of three electronic databases plus hand-searches of relevant papers, identified 26 papers reporting on 16 intervention studies that met the inclusion and exclusion criteria. Interventions varied considerably in their content and duration. A narrative synthesis considers the effectiveness of these interventions on health, family-related and adolescent psychosocial outcomes. The most intensive interventions had the most support, however there is also promising evidence regarding less intense, quarterly psychoeducational and problem-solving interventions. The empirical paper explored the lived experience of eight healthcare professionals’ working with adolescents with T1D and poor adherence to treatment. Data was analysed using interpretative phenomenological analysis and four superordinate themes were identified; “empathy and insight”, “negotiating relationships”, “impact on self” and “coping”. Professionals empathised with the adolescents whilst also being driven by insight of the risks of poor adherence that the adolescents could not comprehend. They valued a close relationship with the adolescents but also had to balance parental involvement. Poor adherence had a personal impact on each professional, including a sense of powerlessness and failure, but also reward. Professionals coped with these experiences in different way, including negotiating when to do more and when to let go. Clinical implications include a potential benefit of acceptance-based training and reflective practice. Contributions to theory and clinical practice considers the overall impact of these findings. Particular reference is made to the systemic factors involved in adolescent diabetes management and the role of clinical psychology within paediatric diabetes teams.