Inclusion Criteria:  Chinese aged 12-24 years old; Informed consent of participation into the study is given by the participant and his/her parent or guardian (for those aged under 18); Being able to comply with the study protocol; Having a DSM-5 diagnosis of insomnia disorder, with a score on Insomnia Severity Index (ISI) >= 9 (suggested cut-off for adolescents)  Exclusion Criteria:  A current diagnosis of substance abuse or dependence; a current or past history of manic or hypomanic episode, schizophrenia spectrum disorders, neurodevelopmental disorders, organic mental disorders, or intellectual disabilities; Having a prominent medical condition known to interfere with sleep continuity and quality (e.g. eczema, gastro-oesophageal reflux disease); Having a clinically diagnosed sleep disorder that may potentially contribute to a disruption in sleep continuity and quality, such as narcolepsy, sleep-disordered breathing, and restless leg syndrome; Concurrent, regular use of medications(s) known to affect sleep continuity and quality (e.g. hypnotics, steroids); In the opinion of the research clinician, having a clinically significant suicidality (presence of suicidal ideation with a plan or an attempt); Having been enrolled in any other clinical trial investigational products within one month at the entry of the study; Initiation of or change in antidepressant medication within past 2 months; Having been or is currently receiving any structured psychotherapy; With hearing or speech deficit; Night shift worker.