A chief component of America's drug war has been increasingly harsh sentences for drug possession and sales, causing the Nation's prisons to fill up with drug offenders, many of whom have substance abuse problems. Also, people with serious mental illness who fall through the cracks of the public mental health system frequently are housed in prisons or jails, often as a result of antisocial behavior or self-medicating with illicit drugs. As more addicted and mentally ill offenders enter the corrections system, correctional officials are increasingly looking at behavioral health care as they try to control the billions of Federal, State, and local dollars being spent on housing and guarding these prisoners. Ideally, corrections-based behavioral health services should encompass a continuum of interventions, including diversion programs that provide nonviolent addicted or mentally ill offenders with alternatives to incarceration. For those who are already incarcerated, residential treatment can lay the foundation for recovery and successful reintegration into society, and effective aftercare can ensure that the lessons learned in treatment take hold and are reinforced in the community. This paper profiles therapeutic communities as the most effective model for treating incarcerated offenders with addiction problems. Strong aftercare and parole programs and services are emphasized as important components of treatment after release from prison. The concluding section of the paper outlines a strategy for "selling" treatment to corrections officials.