Until the early 1990s, much of the research in substance abuse was focused on males or mixed-gender samples without significant attention to gender differences. In 1994, the National Institutes of Health published guidelines concerning the inclusion of women and minorities as subjects in clinical research (National Institutes of Health 1994). Since that time, the number of published research reports examining various aspects of substance use disorders in women and gender differences in substance use disorders has increased tremendously. There is now greater recognition that important biological and psychosocial differences between men and women influence the prevalence, presentation, comorbidity, and treatment of substance use disorders. This increase in awareness of gender-specific issues is also seen in the clinical sector, with approximately 40% of substance abuse treatment facilities now providing special programs or groups for women (Substance Abuse and Mental Health Services Administration 2006a). This chapter provides an overview of the current knowledge base concerning substance use disorders in women. Specifically, the epidemiology, neurobiology, psychiatric comorbidity, course of illness, and treatment of substance use disorders in women is reviewed.