Health risk communication deals with planned or unplanned communication to the public about the nature, impact and management of a wide array of health threats, such as cancer, HIV/AIDS or influenza pandemics. Traditional health risk communication models used to stress a one-way flow of health risk messages to the public. The dominant focus was on experts (government, health organizations, merely disseminating risk information and educating a lay and ignorant public about health threats. However, this simplistic top-down model of communication ignored the complex nature of the audience and the publics understanding of risk information. Fortunately, there has been a shift away from top-down communication about health threats. This book gathers research findings and theoretical reviews with a focus on the role of mass media as sources of health risk information, the role of message formats or frames and risk information source characteristics.