Abstract Substance use disorders (SUDs) continue to be one of the most serious public health problems in the US.1 Studies have consistently documented a substantially higher prevalence of SUDs among adults under justice supervision in the community (i.e., probation/parole) as compared to the general population.2-4 Continuing care initiatives for individuals with SUDs have gained increased attention with the recognition that substance use treatment requires long-term care.15, 46, 47, 54-58 Studies show that continuing care interventions can provide ongoing support or extend primary treatment gains with respect to reductions in substance use, relapse, and criminal activity.12, 52, 55, 56, 61-63 Recent diffusion of Internet and smartphone technologies among disadvantaged populations now offers unprecedented opportunities for increasing access to quality continuing care interventions as well as chronic disease self-management tools. Probationers and parolees at high risk for drug abuse relapse and involvement in health compromising behaviors are an important population that stands to benefit from continuing care technologies. Building on our team’s extensive experience in the fields of criminology and substance use, we propose to finalize the development of a Continuing Care mobile application (app) by enhancing app capabilities and conducting a randomized controlled trial to assess its effectiveness among clients on probation or parole who are enrolled in outpatient substance use treatment. The app is designed to meet the recovery and personal support needs of probationers and parolees with SUDs who are at elevated risk of relapse, treatment discontinuation, re-arrest, and incarceration. It is guided by the principles of the transtheoretical model of behavior change,24 and app content is derived from the Your Own Reintegration System (YOURS) program,25 an empirically-supported26 intervention that focuses on substance use recovery, reducing criminal thinking and behavior, and cultivating support systems. If proven to be effective, the CC app could be deployed across the national network of outpatient treatment providers and be highly significant in its direct impact on public health.