Uncertainty is inherent to science and exploited by those who wish to stymie regulations. Chemical, oil, and tobacco companies kept their products on the marketplace and promoted consumerism by stressing the unsettled nature of research. With us to explore this history, and how it relates to the environment and public health, is Mark Lytle. Mark, the author of important books in environmental history, is among those historians seeking to develop the field of “Environmental Diplomacy.”