Postpartum depression (PPD) affects 1 in 7 mothers in the US with double the rate among low-income women, causing emotional distress, consequences for infant development and later child adjustment, disruptions in family relationships, and significant financial burden. The ROSE Program (Reach Out, Stay Strong, Essentials for mothers of newborns) is an evidence-based preventive intervention administered as a series of 4 in-person group sessions plus one postpartum booster session. ROSE reduced cases of PPD by half in four clinical trials with low- income women. However, there are major obstacles to disseminating ROSE broadly to women at risk for PPD. If women across the nation could easily access ROSE virtually at the time and place of their choosing, the incidence of PPD could be reduced significantly. Our Phase I project developed a prototype of the first virtual ROSE session and we found 100% of 38 pregnant women at risk for PPD who trialed the session rated their experiences as highly favorable, informative, and helpful. Our current Phase II proposal goal is to finish development of a full app-based ROSE program (e-ROSE) and evaluate the app’s outcomes to lay the groundwork for commercialization and broad implementation. We know from previous trials that ROSE has better outcomes than a control consisting of an educational brochure about PPD. We now hypothesize e-ROSE and ROSE delivered as usual (ROSE) will result in better depression outcomes compared to these historical control data. We also hypothesize e-ROSE will result in a better return on investment (ROI) compared to ROSE and compared to utilization data from a second control group of women who were not offered ROSE identified through electronic health records. We will explore if depression outcomes for e-ROSE are non-inferior than for ROSE. Last, we hypothesize that perceived access and satisfaction with the intervention will serve as mediators of depression outcomes. Thus we will complete conversion of all five group sessions to an app-based platform and incorporate additional engagement and support strategies (Aim 1), test its impact on reducing PPD and improving ROI within 3 months post-delivery in a randomized trial (Aim 2), and determine if improving perceived access and satisfaction is a pathway for improving depression (Aim 3). At the end of the project, the e-ROSE product will be ready for Phase III commercialization nationwide allowing easy, low-cost distribution on a variety of platforms to the end-users as well as position us for further research via implementation studies.