Project Abstract Depression affects more than 3.2 million adolescents in the USA, with rising incidence and suicide rates that carry devastating personal, societal, and economic impact. Effective care for adolescent depression is limited due to lack of access, shortage of providers, long waitlists, stigma, and ineffective or partially effective pharmacological options. Many adolescents with depression are initially diagnosed and receive treatment from primary care providers, who, unfortunately, often have limited time, training, and options to be effective gatekeepers for treatment. There is an urgent need for accessible, cost-effective, and clinically-validated treatment options for adolescents diagnosed with depression, particularly in primary care settings. Digital health interventions represent an exciting and promising new direction for mental health treatment with strong potential to increase access to care. Such technology is especially critical and timely during this period of mandated physical distancing, which is expected to increase social isolation and exacerbate difficulties in receiving care. Currently available commercial digital health options widely lack clinical validation, cannot make strong medical claims, and are not specifically designed for adolescents. We aim to develop an FDA-cleared, self-guided, cognitive behavioral therapy (CBT)-based mobile program (Limbix Spark) to be prescribed by primary care providers and psychiatrists and commercialized for at-home patient use as first line treatment. Limbix Spark implements behavioral activation, a key CBT skill that provides a sense of pleasure or mastery through self-monitored activities to reduce depressive symptoms and improve functional outcomes. Given youth ease with and preference for technological solutions, an age-appropriate and engaging mobile intervention can be both beneficial and enjoyable. Building on outcomes from a feasibility trial demonstrating high feasibility and engagement, and preliminary evidence of clinically meaningful reductions in depressive symptoms, in Phase I of the proposed Fast Track, we will conduct rigorous testing to optimize our Limbix Spark program and show high usability, build a regulatory compliant platform, and prepare for a Phase II clinical trial. In Phase II, we will demonstrate clinical effectiveness of Limbix Spark by conducting a double-blind, placebo controlled, randomized clinical trial with patients recruited and enrolled from primary care and psychiatric clinics. The team, led by veteran entrepreneurs, research professionals, industry leaders, and clinical experts, is singularly qualified to conduct the proposed research and commercialize Limbix Spark as an adolescent depression prescription digital therapeutic, accelerating access to care for a severely underserved population.