Risk is perceived and acted on in 2 fundamental ways. Risk as feelings refers to individuals' fast, instinctive, and intuitive reactions to danger. Risk as analysis brings logic, reason, and scientific deliberation to bear on risk management. Reliance on risk as feelings is described with "the affect heuristic." The authors trace the development of this heuristic across a variety of research paths. The authors also discuss some of the important practical implications resulting from ways that this heuristic impacts how people perceive and evaluate risk, and, more generally, how it influences all human decision making. Finally, some important implications of the affect heuristic for communication and decision making pertaining to cancer prevention and treatment are briefly discussed.