The investigators will answer the question of whether treating insomnia using the mobile-app-based intervention of Cognitive Behavioural Therapy for Insomnia (CBT-I) for cancer survivors ("iCANSleep") can improve symptoms of insomnia in Canadian cancer survivors compared to a waitlist control group. The investigators will recruit 146 people with insomnia who have completed cancer treatment at least 3 months prior to the study.

The investigators will conduct a randomized controlled trial of immediate treatment with the CBT-I app "iCANSleep" compared to a delayed treatment group with 146 cancer survivors who have completed primary treatment at least 3 months prior and meet DSM diagnostic criteria for insomnia. Participants who are randomized to the immediate treatment group will complete the 7-modules of the CBT-I treatment right away. Those randomized to the delayed treatment group will begin the intervention following an 8-week waiting period. The treatment group will complete assessments at baseline, mid-treatment, post-treatment, and 3-month follow-up. The delayed treatment group will complete an assessment at baseline, halfway through their wait at 4 weeks, and prior to beginning treatment at 8 weeks. They will also complete assessments at mid-treatment, post-treatment and 3-month follow-up. Insomnia severity will be analyzed using the Insomnia Severity Index (ISI) as the primary outcome. Other measures will include fatigue, anxiety, depression, pain, work productivity, sleep beliefs, daytime impact of insomnia, and pre-sleep arousal.

The investigators hypothesize that the immediate treatment group will report significantly greater improvements in insomnia compared to the waitlist control group at post-treatment (primary endpoint). The investigators also hypothesize that these improvements will be maintained at 3-months follow-up (secondary endpoint).

Inclusion Criteria:

• Cancer survivors
• Over 18 years of age
• Lives in Canada
• Understands English or French fluently
• DSM-5 diagnosis of insomnia
• ISI score of 8 or higher
• Good performance status as indicated by a score of 0-2 on the Eastern Cooperative Oncology Group (ECOG) performance status scale
• Access to internet connection
• Ownership of smartphone
• Fluency using mobile applications.
• Individuals with non-hematological malignancies must show no evidence of cancer or clinically stable/inactive disease for a minimum of 3 months prior to enrollment (for individuals with non-metastatic cancer) or be on a stable treatment regimen for the prior 3 months (for individuals with metastatic cancer) to ensure that insomnia is not a direct, acute response to cancer treatment.
• Individuals with hematological malignancies must be in remission at the time of recruitment and have completed cancer treatments (e.g., transplant, chemotherapy, immunotherapy, radiotherapy) at least 3 months prior.

Exclusion Criteria:

• Presence of a sleep disorder other than insomnia that is not adequately treated (e.g., untreated sleep apnea)
• Presence of a psychological disorder that is currently untreated or would impair the ability to participate (e.g., bipolar disorder)
• Major sensory deficit (e.g., blindness)
• Previous experience receiving CBT-I.
• The use of medications prescribed for sleep (e.g., hypnotics, sedatives, or antidepressants) will be tracked and adjusted for in the statistical analysis.