This project aims to understand and treat insomnia disorder to prevent depression and anxiety. The investigators will use an experimental parallel two-arm repeated measures randomized controlled trial in a cohort of individuals with insomnia to compare the effects of online therapist-guided cognitive behavioural and circadian therapy for insomnia (CBCTi; N=82) versus control (N=27) on subjective and objective sleep and circadian measures as well as symptom and severity of depression and anxiety. The project will involve at-home assessments.Participants from the CBCTi group will also be invited for two sleep studies and neuroimaging sessions to investigate the effects of CBCTi on neuroimaging and psychophysiological markers of overnight regulation of emotional distress.