Despite knowing little about nanotechnology (so to speak), members of the public readily form opinions on whether its potential risks outweigh its potential benefits. On what basis are they forming their judgments? How are their views likely to evolve as they become exposed to more in-formation about this novel science? We conducted a survey experiment (N = 1,850) to answer these questions. We found that public perceptions of nanotechnology risks, like public perceptions of societal risks generally, are largely affect driven: individuals’ visceral reactions to nanotechnology (ones likely based on attitudes toward environmental risks generally) explain more of the variance in individuals’ perceptions of nanotechnology’s risks and benefits than does any other influence. These views are not static: even a small amount of information can generate changes in perceptions. But how those perceptions change depends heavily on individuals’ values. Using a between-subjects design, we found that individuals exposed to balanced information polarize along cultural and political lines relative to individuals not exposed to information. We discuss what these findings imply for understanding of risk perceptions generally and for the future of nanotechnology as a subject of political conflict and regulation.