Inclusion Criteria:  Older adults aged ≥ 60 years Able to give informed online consent Insomnia Severity Index ≥ 10, including a score of 3 in at least one of the first three items (nocturnal symptoms). English fluency Access to a smartphone and willingness/proficiency to use a mobile app  Exclusion Criteria:  Shift-workers Travel to a destination with >2 hours time-difference (within 30-days) Serious medical and/or psychiatric illnesses/disorders or self-harm risk (Patient Health Questionnaire-9, item 9, 1+ score of risk of suicidal ideation) Diagnosed sleep disorders other than insomnia Regular sleep medications or sleep devices (>2 times a week over last 6 months) Currently receiving or previously received (within the last 12 months) psychotherapy for insomnia including Cognitive Behavioural Therapy (CBT). Drive for work/operate heavy machinery