During the past several years, a number of aggressive federal and state initiatives have been undertaken to expand substance abuse treatment within correctional settings. These efforts have been fueled by the high rates of substance involvement among offenders and the growing body of research literature suggesting that intensive, prison-based treatment efforts can significantly reduce postprison substance use and recidivism. However, the rapid expansion of these programs increases their vulnerability to common implementation problems that could lead to pessimistic, and erroneous, assumptions about their effectiveness. This article summarizes both the research literature and the experiences of the authors regarding six common barriers to developing effective correctional treatment programs and offers potential solutions for each.Primarily as a result of increased vigilance and mandatory sentences, state and federal criminal justice systems in the United States have witnessed substantial growth in the proportions of their populations who are serving time for drug-specific or drug-related crimes. From 1980 to 1995, drug law violators _____________________________________________________________