Insomnia is one of the most common sleep disorders and affects approximately 10 - 40% of the population across different age groups in Hong Kong. Cognitive behavioral therapy for insomnia (CBT-I) is the first line treatment for adult insomnia due to its comparable effect to medication in short term but is more sustainable in the long run. However, only a few sufferers have received CBT-I, due to limited accessibility, lack of trained sleep therapists, time costing and geographical limitations. To increase CBT-I accessibility, different formats of CBT-I have been proposed. Empirical evidence including ours consistently suggested that self-help digital CBT-I is effective in improving sleep while its augmentation with a guided approach could further enhance the treatment gain. Previous evidence has suggested that although self-help CBT-I could lead to positive outcomes, the drop out rate is quite high and maybe less effective for patients with comorbidity or high level of distress. Thus, a stepped-care approach to CBT-I that utilizes online self help and therapist-guided modes of delivery might be a potential way to facilitate efficient dissemination of effective insomnia treatment resources. The effectiveness of the stepped care model will be evaluated in a real world setting using stepped-wedge cluster randomized controlled design. The program will be rolled out to different districts in Hong Kong sequentially in 18 districts over 4 steps with a eqaully spaced time periods.