We sought to obtain evidence about the scope of women's empowerment and the mechanisms underlying the significant reduction in intimate partner violence documented by the Intervention With Microfinance for AIDS and Gender Equity (IMAGE) cluster-randomized trial in rural South Africa. The IMAGE intervention combined a microfinance program with participatory training on understanding HIV infection, gender norms, domestic violence, and sexuality. Outcome measures included past year's experience of intimate partner violence and 9 indicators of women's empowerment. Qualitative data about changes occurring within intimate relationships, loan groups, and the community were also collected. After 2 years, the risk of past-year physical or sexual violence by an intimate partner was reduced by more than half (adjusted risk ratio=0.45; 95% confidence interval=0.23, 0.91). Improvements in all 9 indicators of empowerment were observed. Reductions in violence resulted from a range of responses enabling women to challenge the acceptability of violence, expect and receive better treatment from partners, leave abusive relationships, and raise public awareness about intimate partner violence. Our findings, both qualitative and quantitative, indicate that economic and social empowerment of women can contribute to reductions in intimate partner violence.