Risk communication, the specialized practice of publicly communicating the impact of an existing activity or future technology to the public's health or the environment, is largely based on a transmission model of communication. Although its practice originated in the early 20 th century in local public warnings about natural disasters, contemporary risk communication covers a multitude of issues from natural, health, industrial hazards to new, controversial technologies, such as genetically modified foods. As discourse aimed at gaining public consent or trust on a contested issue of social values, risk communication is essentially moral in nature, and as such, must proceed from a conception of public discourse that provides a moral grounding. I argue that the transmission model of communication, governed by norms of efficiency, is incapable of providing a vocabulary or conceptual framework for the moral nature of these debates, particularly broad social risks. Such a conception, I argue, can be accomplished by viewing risk communication through the lens of rhetorical theory, which finds its justification as moral discourse in the definition of the public as citizens engaged in social decision-making and meaning formation. Viewed from the perspective of rhetorical theory, risk communication functions as ethical public discourse, not from the unmotivated perspective of its source, but from the manner in which it makes itself open to public examination and debate.