Opioid use disorders (OUDs) are a significant and growing public health issue; over a third of persons seeking substance abuse treatment have an OUD and the annual cost of OUDs is over $30 billion. Methadone maintenance treatment (MMT) has been widely shown to be safe and effective in treating OUDs, especially when evidence-based psychosocial interventions are part of treatment. Unfortunately, MMT programs offer the lowest level of psychosocial treatment relative to other types of drug treatment programs. The current application is being submitted under the Behavioral & Integrative Treatment Development Program (PA 07- 111). Aim 1 is to develop a Mobile Therapeutic System (MTS) that offers key elements of an evidence-based psychosocial intervention (Community Reinforcement Approach; CRA) including Goal Setting and Monitoring, Functional Analysis of Drug Use, Self-Management, Drug Refusal Skills, Problem-Solving, and Social and Recreational Counseling. Participants will be provided unlimited daily prompts to encourage program use and will be provided with unlimited access to the mobile application. Our iterative development process will include input from focus groups with clients in MMT (n=24), input from experts in the field, and feedback from clients in MMT (n=30) on a beta-version of the mobile phone-based program. Aim 2: We will evaluate the efficacy of this mobile tool with participants entering methadone maintenance treatment (MMT) during the first three months of their treatment (n=219). We will evaluate the relative preliminary efficacy of (1) standard treatment, (2) standard treatment plus MTS and (3) a mobile-based control condition on the primary outcomes of treatment retention and opioid use (via urine toxicology) and secondary outcomes of other substance use (via urine toxicology and self-report), readiness to change drug use behavior, coping skills, opioid craving, HIV risk behavior, and psychosocial functioning during the 3-month intervention phase. Durability of effects will be examined at 1 and 3 month follow-ups. To our knowledge, this study would be the first to use mobile phone technology to deliver a comprehensive, interactive, evidence-based psychosocial intervention targeting illicit drug use that can be easily accessed in an individual's natural environment and provide treatment on-demand. Aim 3: We will perform an economic analysis of MTS in community-based MMT. We will estimate the incremental costs and the incremental cost-effectiveness ratio (ICER) of MTS relative to standard care and the mobile control group. The primary ICER will consider costs per increased abstinence time (clinical efficacy) and the secondary ICER will consider costs per increased quality adjusted life year (economic efficacy). Cost data are vital to future translationl projects to disseminate effective mobile interventions in community systems. If results are promising, MTS would be easily adaptable and may have enormous impact on improving treatment access and effectiveness for a variety of issues (e.g., mental and behavioral health) while significantly limiting costs.