Two decades of experience and research provide new insights into the role of condoms for AIDS prevention in the developing world. This literature review and synthesis is based on computerized searches of the scientific literature and review of conference presentations, publications of national and international organizations, and popular media. Condoms are about 90 percent effective for preventing HIV transmission, and their use has grown rapidly in many countries. Condoms have produced substantial benefit in countries like Thailand, where both transmission and condom promotion are concentrated in the area of commercial sex. The public health benefit of condom promotion in settings with widespread heterosexual transmission, however, remains unestablished. In countries like Uganda that have curbed generalized epidemics, reducing the number of individuals' sex partners appears to have been more important than promoting the use of condoms. Other countries continue to have high rates of HIV transmission despite high reported rates of condom use among the sexually active. The impact of condoms may be limited by inconsistent use, low use among those at highest risk, and negative interactions with other strategies. Recommendations include increased condom promotion for groups at high risk, more rigorous measurement of the impact of condom promotion, and more research on how best to integrate condom promotion with other prevention strategies.