Sleep disturbance in military Veterans with PTSD is a complex condition, typically characterized by insomnia and nightmares, and frequently accompanied by comorbid obstructive sleep apnea. Each of these problems are shown to influence the others, contributing to a complex sleep disturbance with profound impacts on daytime functioning and quality of life. A vicious cycle in which nighttime disturbances impact daytime functioning, and vice versa, often ensues. Addressing sleep disturbance in Veterans with PTSD therefore requires a multipronged approach that is tailored to each Veterans' constellation of symptoms and each Veterans' goals for sleep health. The Transdiagnostic sleep and circadian intervention (TranS-C), developed by sleep researchers Allison Harvey, Ph.D. and Daniel Buysse, M.D., involves a patient-centered, module-based, flexibly structured approach that tackles numerous sleep disturbances using evidence-based strategies with the overall goal of improving sleep and improving sleep-related impairments in daytime functioning. It is thus well-suited for tackling sleep disturbances and the associated impairments in social, occupational and overall functioning in Veterans with PTSD. The proposed study is a randomized, controlled clinical trial examining the effectiveness of a modified TranS-C intervention for Veterans with PTSD. The modified approach, referred to as TranS-C for PTSD (TSC-PTSD) elevates the importance of nightmare-focused, apnea-focused, and insomnia-focused modules relative to the standard intervention, incorporates an evidence-based relaxation module, and modifies the nightmare and apnea modules based on strategies used for Veterans in the VA healthcare system. The study will administer TSC-PTSD remotely to Veterans in their homes using a VA-approved video-conferencing platform. The study will recruit male and female U.S. military Veterans aged 18 and above throughout California and compare change in a comprehensive measure of daytime functioning and change in insomnia, nightmare and overall PTSD symptoms in participants randomized to the active intervention TSC-PTSD vs. participants randomized to a sleep psychoeducation control (SPC) intervention. The widely used and validated World Health Organization Disability Assessment Schedule (WHODAS) will serve as the primary outcome measure. The Insomnia Severity Index (ISI) and the Clinician-Administered PTSD Scale (CAPS) will be used to measure secondary outcomes. Eligible participants will have an insomnia diagnosis, a PTSD diagnosis (or moderate symptoms of PTSD in the absence of a full diagnosis), and clinically significant nightmares based on gold-standard clinician-administered interviews. All participants will complete baseline surveys related to daytime functioning and sleep-related symptoms prior to treatment initiation, and will complete these surveys again in week 5, and at the end of treatment. For additional high-resolution data on sleep patterns, all participants will record sleep-related information, including nightmare occurrence and severity, in the morning and at bedtime using a Veteran-tested and user-friendly sleep diary mobile app. Participants will also complete the clinical interview and self-report surveys at 3-month and 6-month follow-up, to assess the durability of treatment effects. The duration of TSC-PTSD may vary between a minimum of 8 and a maximum of 12 sessions and the psychoeducation control protocol will involve 10 sessions. The hypotheses are: 1) subjects randomized to TSC-PTSD will demonstrate greater improvement in WHODAS score relative to SPC from baseline to post-treatment; 2) subjects randomized to TSC-PTSD will demonstrate greater improvements in insomnia, nightmares and PTSD symptoms as demonstrated by improvements in the ISI, CAPS distressing dreams score, and CAPS total score relative to SPC from baseline to post-treatment; and 3) subjects randomized to TSC-PTSD will demonstrate greater sustained improvement in functional and clinical outcomes at 3-month and 6-month follow-up relative to SPC, and improvements in WHODAS score will be mediated by improvements in ISI, nightmares and TranS-C indicators of sleep health in both study groups. Findings in support of the investigators' hypotheses will provide a vital new tool for advancing rehabilitation in U.S. military Veterans with PTSD.