This brief, from the CSG Justice Center, is designed to help state and local officials better support young adults in the justice system. It identifies these young adults’ distinct needs, summaries the limited research available on what works to address these needs, and provides recommendations for steps that policymakers, juvenile and adult criminal justice agency leaders, researchers, and the field can take to improve outcomes" (website). Part I—How Young Adults Are Developmentally Different from Youth and Older Adults: how young adults are distinct from youth; how young adults are distinct from adults; and young adults by the numbers--arrest rates, incarceration rates, and recidivism rates. Part II—Opportunities and Challenges to Meeting Young Adults' Needs: young adults under justice system supervision have distinct needs and few programs exist that are proven to effectively meet these needs—criminal thinking and behavior, education, employment, mental health and substance use, and transition to independence; young adults face systemic barriers to meeting their needs—aging out of protective networks and lack of coordination across service systems, and collateral consequences. Part III—Recommendations: four recommendations; and promising models for young adults under justice system supervision—Multisystemic Therapy for Emerging Adults (MST-EA), and the Roca nonprofit organization in Massachusetts; and increasing cross-systems coordination to improve outcomes for young adults in Iowa—the Iowa Collaboration for Youth Development (ICYD).