America’s jails and prisons are at the epicenter of illicit substance use and misuse. Nationally, nearly one in five people entering local jails has an opioid use disorder (OUD), and some states estimate that a majority of their residents with OUDs pass through the doors of their jails each year. Many of these individuals also have co-occurring mental disorders. Universal screening for substance use and co-occurring disorders for persons entering jails and prisons, and assessment as indicated, is an opportunity to connect individuals to evidence-based treatment services while incarcerated and ensure continuity of care upon reentry to the community. Medication-assisted treatment (MAT)—the use of the FDA-approved medications buprenorphine, naltrexone, and methadone—is the standard of care for individuals with OUD. MAT has been demonstrated to reduce illicit drug use post-release and to lower recidivism rates. However, MAT access is limited in most communities and absent in many jails, resulting in a significant missed opportunity to provide treatment to individuals with OUD.