The paper is intended primarily for treatment providers and researchers. Written primarily from the perspective of individual treatment, the paper emphasizes the recent literature published in the United States, primarily over the past 10 years. The first section of the paper provides a context by briefly reviewing the nature of the problem, its prevalence, and definition. The second section reports on the findings of a survey of treatment, following three trajectories. First, the essential features of dual disorder and guidelines for treatment are placed in historical perspective. Next, three approaches of particular promise -- comprehensive integrated treatment, assertive community treatment, and the modified therapeutic community -- are described and analyzed in some detail. Finally, a summary of treatment models or approaches that warrant further development and study is provided. The third section of the paper discusses "best practices" common to many approaches, as derived from clinical and research literature, as well as from the experiences of the author. This section is included to provide some signposts for program staff, whose response to this population must be informed by the current state of knowledge. The fourth and final section of the paper provides a research agenda that considers both current concerns and emerging issues in this dynamic area. 1 table and 129 references