MISSION-CJ is a comprehensive support model for people with co-occurring mental health and substance use disorders, combining treatment, recovery services, and proactive outreach. Early evidence shows it can improve treatment engagement, enhance mental health, and reduce jail returns. The Supporting Treatment Access and Recovery in Re-Entry (STAR-R) study compares MISSION-CJ to peer linkage support (PLS) to determine whether MISSION-CJ leads to greater treatment participation, reduced substance use and overdose risk, better mental health, and fewer legal problems. Researchers also examine factors that shape these outcomes, such as distancing from negative influences and strengthening community connections. The study further assesses the cost of implementing MISSION-CJ and evaluates its cost-effectiveness relative to PLS and traditional reentry supports.