Circuit parties are weekend-long, erotically charged, drug-prevalent dance events attended by up to 25,000 self-identified gay and bisexual men who socialize and dance nonstop, sometimes for 24 hours or longer. Although these parties started originally as part of the gay community's response to raise HIV/AIDS awareness and to build community and cultural identity, they may have become a site for transmitting HIV across geographical regions and socioeconomic groups of gay and bisexual men. This article reviews the descriptive published studies on circuit parties. The authors use these studies and the literature on drug use and high-risk sexual behavior in gay and bisexual communities, along with sociological and social psychological research, to propose a causal model of why circuit parties may contribute to unsafe sexual practices that increase HIV infection risk. The authors abstract 5 prevention messages relevant to circuit parties and review intervention studies in nonparty settings for insight into how to reduce risky sexual behavior within circuit events. These intervention studies help to identify 5 context-specific groups that can effectively carry the prevention messages. The 5-by-5 matrix represents a first stage in developing a causal model for reducing HIV infections, along with evaluable principles of intervention, at circuit parties.