Gender differences in substance use disorders (SUDs) and treatment outcomes for women with SUDs have been a focus of research in the last 15 years. This article reviews gender differences in the epidemiology of SUDs, highlighting the convergence of male/female prevalence ratios of SUDs in the last 20 years. The telescoping course of SUDs, recent research on the role of neuroactive gonadal steroid hormones in craving and relapse, and sex differences in stress reactivity and relapse to substance abuse are described. The role of co-occurring mood and anxiety, eating, and posttraumatic stress disorders is considered in the epidemiology, natural history, and treatment of women with SUDs. Women's use of alcohol, stimulants, opioids, cannabis, and nicotine are examined in terms of recent epidemiology, biologic and psychosocial effects, and treatment. Although women may be less likely to enter substance abuse treatment than men over the course of the lifetime, once they enter treatment, gender itself is not a predictor of treatment retention, completion, or outcome. Research on gender-specific treatments for women with SUDs and behavioral couples treatment has yielded promising results for substance abuse treatment outcomes in women.