ABSTRACT Adults incarcerated in the United States are disproportionately affected by substance use disorders and chronic physical and mental conditions, and have a high risk of death after release from prison. Medicaid coverage for formerly incarcerated adults increases access to care, but is likely insufficient by itself to substantially improve outcomes without attending to the numerous social and structural barriers that make accessing care difficult. Prior research demonstrates that formerly incarcerated adults under-utilize routine, outpatient health care during the transition from prison to community living, suggesting a dire need for systems-level interventions aimed at improving engagement in primary care. In a prior study funded by NIDA, our team developed a hybrid, in-person and telephone-based nurse case management intervention that bridges the pre-release and post-release period and conducted a single-arm pilot trial in two Wisconsin state prisons. We found that the likelihood of an outpatient care visit shortly after release among those who received the intervention was nearly double the baseline rate, while being highly acceptable to prison staff. In the proposed Renewal Application, we will conduct a two-arm, randomized clinical trial among incarcerated adults with a history of substance use, that compares previously piloted transitional case management intervention, called CJC-TraC, to an enhanced usual care condition consisting of routine multi-disciplinary release planning and provision of a free cellphone at the time of release. The primary and secondary trial outcomes are attending an outpatient visit within 60-days of release for any cause and for a substance use disorder respectively. In the proposed study’s second aim, we will leverage novel linked administrative data and observational research methods to investigate care transition research questions that are policy-relevant but cannot be pursued in a randomized trial of incarcerated adults: estimating the relative effectiveness of the trial arms to usual care; assessing the generalizability of trial results to the target population; and measuring the association between post-release outpatient care use and longer-run health and criminogenic outcomes. Improving access to post-incarceration health care is a major federal policy priority. In 2023, the Centers for Medicare and Medicaid services published Section 1115 Medicaid demonstration waiver guidelines for states to provide Medicaid coverage and care transition services to incarcerated individuals during the pre-release period and post-incarceration. The waiver program represents an unprecedented opportunity to bring care transition services for incarcerated individuals to scale; however, there is limited information identifying what constitutes an effective and scalable care transition program. By testing the effect of a prison system-based intervention able to be replicated and scaled up across multiple settings, findi...