The objective of this randomized controlled trial of the Insomnia Coach mobile app is to evaluate the potential effects of app use on reducing insomnia symptoms among Veterans with significant insomnia and PTSD symptoms. It is also intended to evaluate the impact of the app on other outcomes, including PTSD, depression, and anxiety symptoms, and psychosocial functioning. Finally, the study is designed to assess perceptions of Insomnia Coach regarding its perceived helpfulness, satisfaction, and likes/dislikes to inform its continued improvement. The results of this study will inform the next steps of research evaluating Insomnia Coach with Veterans with significant insomnia and PTSD symptoms, namely a larger-scale, VA ORD or NIH funded randomized controlled trial.