The studies reported in this special issue were designed to take advantage of the unique opportunity that the Criminal Justice Drug Abuse Treatment Studies (CJDATS) cooperative provides to the systematic study of several key issues in programming for co-occurring disorder(s) (COD) in the criminal justice system. These papers present findings from CJDATS studies pertaining to co-occurring disorder(s), identify clinical initiatives to strengthen efforts to treat the population with co-occurring disorder(s), and point to a direction for the elaboration of a future research agenda. Four key areas of investigation are presented: Screening and Diagnosis; the Relationship of Co-Occurring Disorder(s) to Violence; Gender Differences; and the Delivery of Services for Co-Occurring Disorder(s). The first section of this article summarizes the studies included in this special issue within the context of the research literature already available. The second section suggests a future research agenda for the study of offender populations with co-occurring disorder(s), and concludes with a broad statement of clinical advancements to date. Copyright © 2008 John Wiley & Sons, Ltd.