This study aims to examine the efficacy of group-based CBT-I and app-based CBT-I (developed by a group of psychiatrist and clinical psychologists) in reducing insomnia severity in adolescents, when compared with the waiting-list control. This study also examines the effects of group-based CBT-I and app-based CBT-I on the measures of mood symptoms and daytime functioning (e.g. sleepiness, fatigue), as well as subjective and objective sleep measures.