Nanotechnology is science and engineering resulting from the manipulation of matter's most basic building blocks: atoms and molecules. As such, nanotechnology promises unprecedented control over both the materials we use and the means of their production. Such control could revolutionize nearly every sector of our economy, including medicine, defense, and energy. Despite the relatively recent emergence of this field, it already enjoys generous federal funding and enthusiastic media coverage. The tenor of discourse on nanotechnology is changing, however, as the voices of critics begin to sound about a host of concerns ranging from the societal impacts of improving human performance to the specter of environmental devastation and human disease.