Veterans of the most recent wars in Afghanistan and Iraq (collectively, post 9/11 Veterans) have notable sleep problems including chronic insomnia. Here, the investigators plan to compare two groups of veterans with insomnia: (1) one group that completes a 6 week self-management-guided use of a mobile app based on cognitive behavioral therapy for insomnia (CBTI alone) and (2) one group that completes a 6 week combined self-management-guided use of the mobile CBTI app in addition to a physical activity (PA) intervention (CBTI + PA). The investigators hypothesize that the group receiving the adjunctive 6-week PA intervention will have better subjective and objective sleep, higher step counts, and better functional health and social and community integration than those receiving CBTI alone. This pilot work will provide evidence to guide the design of a future randomized controlled trial.

To determine if the addition of physical activity (PA) to (CBTI) can further enhance sleep, physical activity, functioning, or social engagement over and above self-management use of a CBTI app alone, the investigators will randomly assign post-9/11 veteran participants with chronic, functionally impairing insomnia to either (1) a self-management-based use of an app based on cognitive behavioral therapy for insomnia (CBTI; CBTI alone arm) or to (2) a self-management-based use of the CBTI app + a physical activity (PA) intervention (CBTI + PA) that includes PA monitoring (via a Fitbit device) with individualized goal-setting to encourage increased daily steps across the 6 weeks. For the PA goal, the investigators will attempt to get all participants to at least the typical 10,000 daily steps goal cited as a strong predictor of positive health outcomes (Choi, Pak, & Choi, 2007). The investigators will tailor the step goals based on the person's initial level of daily steps, and increment step goals weekly to maximize motivation and enhance the likelihood that the participant can meet the goal.

Inclusion Criteria:

• Eligible individuals will be US military Veterans
• Eligible veterans will have served in the military during the post-9/11 period
• Eligible veterans will have chronic, functionally impairing insomnia (i.e., at baseline veterans must have an Insomnia Severity Index score > 10 with insomnia duration of at least 1 month, and impaired daytime functioning.
• Eligible individuals must be willing to use devices (e.g., Fitbit, WatchPAT)provided by the study team.
• Eligible individuals may have mild or moderate obstructive sleep apnea (as determined by one out of either of two nights with a WatchPAT-based Apnea-Hypopnea Index [AHI] <= 30 events/hour of sleep).

Exclusion Criteria:

• Periodic leg movements
• Circadian rhythm disorder
• Use of medications or health issues (e.g., permanent pacemaker, sustained non-sinus cardiac arrhythmias, finger deformity, etc.) that would interfere with the use of the WatchPAT sleep monitor
• Severe obstructive sleep apnea (as determined by one out of either of two nights with a WatchPAT-based Apnea-Hypopnea Index [AHI] > 30 events/hour of sleep)