OBJECTIVES:To describe the protocol of a randomized controlled trial to evaluate the effectiveness and mechanisms of three behavioral interventions. METHODS:Participants will include up to 343 Veterans with chronic pain due to a broad range of etiologies, randomly assigned to one of three 8-week manualized in-person group treatments: (1) Hypnosis (HYP), (2) Mindfulness Meditation (MM), or (3) Education Control (EDU). PROJECTED OUTCOMES:The primary aim of the study is to compare the effectiveness of HYP and MM to EDU on average pain intensity measured pre- and post-treatment. Additional study aims will explore the effectiveness of HYP and MM compared to EDU on secondary outcomes (i.e., pain interference, sleep, depression, anxiety and PTSD), and the maintenance of effects at 3- and 6-months post-treatment. Participants will have electroencephalogram (EEG) assessments at pre- and post-treatment to determine if the power of specific brain oscillations moderate the effectiveness of HYP and MM (Study Aim 2) and examine brain oscillations as possible mediators of treatment effects (exploratory aim). Additional planned exploratory analyses will be performed to identify possible treatment mediators (i.e., pain acceptance, catastrophizing, mindfulness) and moderators (e.g., hypnotizability, treatment expectations, pain type, cognitive function). SETTING:The study treatments will be administered at a large Veterans Affairs Medical Center in the northwest United States. The treatments will be integrated within clinical infrastructure and delivered by licensed and credentialed health care professionals.