Inclusion Criteria  Stage 1:  Age > 18 years. Informed consent to Stage 1 of the study Diagnosis of Stage I, II or III breast cancer within the previous 12 months  Stage 2:  Informed consent to Stage 2 of the study Current Sleep Disturbance; a score of 8 or more on the Insomnia Severity Index. History of sleep disturbance prior to the screening/baseline consultation; with beginning or worsening of sleep disturbance since breast cancer diagnosis e.g. sleep problems began or get worse with the diagnosis of breast cancer or with chemotherapy. Possession of a suitable smartphone that participant can use independently.  Exclusion Criteria:  Stage 1:  Participants who have limited or no understanding of spoken and/or written English. Other diagnosis of cancer, not including basal cell carcinoma of the skin or cervical carcinoma in situ, within the previous 5 years  Stage 2:  Co-morbidities incompatible with study participation e.g. that result in a participant being unable to complete daily entries satisfactorily via his/her smartphone. Known and/or treated sleep apnoea Regular shift work or night work (defined as >1 overnight shift per month) Breast feeding