Study Design Overview: Male and female subjects from Active Duty, Reserves, National Guard and/or Veterans with a diagnosis of PTSD will be prospectively randomized 1:1 to receive either MBSR Group therapy or Present Centered Therapy (PCGT) Group (control) for 8 weeks. A cluster of at least 12 participants will be randomized individually to either MBRS or PCGT group therapies, which results in at least 6 participants in each intervention group. A total of 30 groups (15 MBSR Groups and 15 PCGT Groups) are anticipated across three clinical research sites involving at least three different MBSR and three different PCGT instructors/therapists. Outcome assessments (single-blind CAPS and self-report measures) will be obtained at baseline, week 3, week 6, and week 9 (primary endpoint). These assessments will be repeated post-acute treatment at week 16 as an exploratory measure of short-term durability effects.