The study aims to evaluate, via a randomised controlled trial (RCT), the effectiveness of Rebound, a moderated online social networking system in preventing relapse of Major Depressive Disorder (MDD) in young people (aged 14-27) with remitted MDD. Rebound includes therapeutic activities and information about mental health, mindfulness, personal strengths, and other topics relevant for young people recovering from MDD. Rebound also includes a social network where participants can communicate via posts and comments in a newsfeed and a problem-solving forum. The social network will be moderated by experienced mental health workers and trained peer workers with lived experience of mental ill-health. Enhanced TAU includes access to a private website with information about depression symptoms, causes and course, the relationship between behaviour and mood, information on diet, exercise, sleep, social support and getting support. Enhanced TAU does not include therapist support or online social networking. The primary hypothesis of the study is that, relative to enhanced TAU, TAU plus Rebound will reduce relapse rates among remitted young people with MDD.