Until effective vaccines against human immunodeficiency virus (HIV) are avail­ able for general public use, the major public health strategy for limiting the spread of acquired immunodeficiency syndrome (AIDS) will be through educa­ tion about the risks of AIDS and instruction in strategies for reducing that risk. But developing effective educational programs requires a deeper understanding of how people think about the risks of AIDS and how they make decisions regarding those risks. Studies of risk perception and risk-taking behavior in other domains have identified a number of systematic biases in people’s risk percep­ tions and decision-making processes. These behavioral biases may lead people to make poor decisions that affect their risk of acquiring or spreading HIV infec­ tion. They also pose a significant obstacle to attempts to develop effective risk communications regarding AIDS and transmission of HIV.