The traditional US heroin market has transformed into a broader illegal opi- oid market, dominated first by prescription opioids (PO) and now also by fentanyl and other synthetic opioids (FOSO). Understanding of opioid-use disorder (OUD) has also transformed from being seen as a driver of crime to a medical condition whose sufferers deserve treatment. This creates new challenges and opportunities for the criminal justice system (CJS). Address- ing inmates’ OUD is a core responsibility, including preventing overdose after release. Treatment can be supported by diversion programs (e.g., drug courts, among others) and by providing medication-assisted treatment in prison, not only as a crime-control strategy but also because of ethical and legal responsibilities to provide appropriate healthcare. The CJS also has opportunities to alter supply that were not relevant in the past, including deterring pill-mill doctors and disrupting web sites used to distribute FOSO.