PTSD occurs in up to 17% of post-9/11 US Service Members and is associated with long-term functional impairment, family problems, unemployment, and suicidality. Trauma-focused therapies (TFTs), such as Prolonged Exposure (PE), result in significant relief for many. Yet, TFTs are not equally effective for everyone. An important minority (\~40%) will retain their PTSD diagnoses after treatment, and many discontinue treatment prematurely, especially post-9/11 Service Members. TFTs are also more effective in addressing symptoms than psychosocial functioning. More work is needed to improve the consistency and potency of TFTs. Partnering with significant others may provide a powerful method for helping individuals get more out of their PTSD treatment. Observational research shows that relationship factors can help patients initiate, stay in, and experience greater benefit from PTSD treatment. Veterans that were surveyed experienced greater treatment gains when they shared more about their treatment with loved ones and when loved ones accommodated less for PTSD symptoms. Despite the promise of partner-involved interventions, there is no couples approach to PTSD treatment that has demonstrated superior outcomes to individual-only treatment models (i.e., TFTs). To address this gap, the investigators have completed a series of partner-assisted PTSD treatment studies, leading up the current proposal (Partnered PE, PPE). The investigators found that treatment completion rates were better than routine clinical care, and the treatment led to large improvements in participants' functioning, PTSD symptoms, and romantic functioning. For this proposed study, the primary objective is to conduct a randomized controlled trial (Research Level 3; larger-scale clinical trial) to test the superiority of PPE to standard PE among post 9/11 Veterans. The investigator's primary hypothesis is that PPE will lead to greater improvements in psychosocial functioning than standard PE. Secondary and tertiary aims examine posttreatment clinical outcomes (PTSD, depression) and intimate partner outcomes (relationship functioning, distress, caregiver burden, and psychosocial functioning), as well as examine strategies for PPE implementation. In exploratory aims, the investigators will examine the stability of group differences, treatment completion rates, the role military sexual trauma history, and treatment mechanisms.