Inclusion Criteria:  Age 18+ years Provided informed consent Ability to read and write in Portuguese Ability to use a computer and/or smartphone, and the internet History of cancer, any type or stage An interval of 1 or more months from the end of active treatment (chemotherapy and/or radiotherapy) Subclinical or significant symptoms of insomnia (ISI scores>8) and positive screen for probable ICSD-3 insomnia disorder Ongoing sleep medication only accepted if the dosage has been stable during the last 3 months No participation in any other interventional study or clinical trial  Exclusion Criteria:  Age ≤ 18 years Absence of clinically or subclinical significant symptoms No history of cancer Inability to provide informed consent Inability to use a computer and/or smartphone No access to the internet Another untreated sleep diagnosis Current major psychiatric or medical condition Pregnancy Parallel ongoing psychological treatment for insomnia Habitual night shift, or rotating shift-workers