Background and Significance: Obsessive-compulsive disorder (OCD) is a chronic and debilitating psychiatric disorder affecting approximately 170,000 Veterans in the VHA. OCD involves obsessions (unwanted, intrusive thoughts) and compulsions (repetitive mental or physical actions aimed at reducing distress). Individuals with OCD experience significant functional impairments and have an increased odds for reporting a lifetime history of suicide attempts. Despite the prevalence and functional impairment associated with OCD, few Veterans with this condition receive Exposure and Response Prevention (ERP), the gold-standard intervention for OCD. ERP is a behavioral treatment in which individuals are systematically exposed to feared situations that elicit distress associated with OCD symptoms. In the VA, Veterans with OCD have a 2% chance of receiving this treatment. To date, there is no data on the effectiveness of ERP for OCD in Veterans. The parent trial seeks to evaluate the effectiveness of telehealth-delivered ERP for OCD in Veterans compared to a control condition, telehealth- delivered Stress Management Training (SMT), within a hybrid type 1 effectiveness-implementation trial. Primary outcomes include changes in functioning and secondary outcomes include the evaluation of ERP's potential for implementation. In addition to evaluating the effectiveness of ERP, mixed-method economic evaluations can help VA stakeholders evaluate tradeoffs between multiple strategies to address OCD in Veterans and identify which interventions may have the greatest potential for adoption and sustainability. Within mixed-method economic evaluation, quantitative analysis would include evaluating the health utilities of Veterans with OCD (values associated with a particular health state) and a cost-effectiveness analysis (i.e., a comparison of the difference in intervention costs to outcomes in OCD symptoms). Qualitative interviews would provide information regarding context-specific factors affecting resources related to ERP delivery. Thus, the aims of the current supplement are to understand the baseline health utility of Veterans with OCD as an indicator of relative disease burden, to conduct a preliminary CEA of ERP for OCD, and conduct a qualitative analysis of economic and resource-related factors as they pertain to ERP delivery. Research Plan: Aim 1: Evaluate the health utility of Veterans wit OCD. This will be achieved by applying an algorithm to the Veterans RAND-12, a generic measure of health-related quality of life. Aim 2: To conduct a cost effectiveness analysis of ERP for changes in Quality Adjusted Life Years and OCD symptoms. This will be achieved by micro-costing the ERP and SMT interventions to obtain an incremental cost-effectiveness ratio of the difference in costs compared to difference in outcomes (i.e., OCD symptoms and Quality Adjusted Life Years). Aim 3: To evaluate the contextual factors impacting the cost and resources required for ERP implement...