Why do people often sharply disagree about things that scientists mostly agree on? As Kahan has written, “The same groups who disagree on 'cultural issues' — abortion, same-sex marriage and school prayer — also disagree on whether climate change is real and on whether underground disposal of nuclear waste is safe.” How could views on such divergent issues go together? Kahan and his colleagues are looking at something they call the “cultural cognition of risk” to explain why individuals form opinions at odds with the facts. People’s assessment of risk—and even their willingness to admit the existence of a scientific consensus—depends upon their values. In one survey, 80 percent of the respondents said they knew little or nothing about nanotechnology—but 90 percent had strong opinions about the risks! Kahan has shown that “experts” who seem to share the values of their audience are judged to be much more persuasive than experts who seem to have different values. He will tell us how his studies shed light on the origins of America’s scientific culture wars, and, if we press him, he might also talk about his findings on public perception of gay and lesbian parenting, and on the likely course of synthetic biology risk perception.