•The Insomnia Coach mobile app is a scalable, self-guided method to deliver CBT-I.•Veterans with insomnia symptoms found the app feasible and acceptable to use.•Insomnia Coach showed improvements on select sleep and mental health symptoms. Insomnia is highly prevalent among military veterans but access to cognitive-behavioral therapy for insomnia (CBT-I) is limited. Thus, this study examined the feasibility, acceptability, and potential efficacy of Insomnia Coach, a CBT-I-based, free, self-management mobile app. Fifty U.S. veterans, who were mostly male (58%) and mean age 44.5 (range = 28–55) years with moderate insomnia symptoms were randomized to Insomnia Coach (n = 25) or a wait-list control condition (n = 25) for 6 weeks. Participants completed self-report measures and sleep diaries at baseline, posttreatment, and follow-up (12 weeks postrandomization), and app participants (n = 15) completed a qualitative interview at posttreatment. Findings suggest that Insomnia Coach is feasible to use, with three quarters of participants using the app through 6 weeks and engaging with active elements. For acceptability, perceptions of Insomnia Coach were very favorable based on both self-report and qualitative interview responses. Finally, for potential efficacy, at posttreatment, a larger proportion of Insomnia Coach (28%) than wait-list control participants (4%) achieved clinically significant improvement (p = .049) and there was a significant treatment effect on daytime sleep-related impairment (d = −0.6, p = .044). Additional treatment effects emerged at follow-up for insomnia severity (d = −1.1, p = .001), sleep onset latency (d = −0.6, p = .021), global sleep quality (d = −0.9, p = .002), and depression symptoms (d = −0.8, p = .012). These findings provide preliminary evidence that among veterans with moderate insomnia symptoms, a CBT-I-based self-management app is feasible, acceptable, and promising for improving insomnia severity and other sleep-related outcomes. Given the vast unmet need for insomnia treatment in the population, Insomnia Coach may provide an easily accessible, convenient public health intervention for individuals not receiving care.