The combination of the burgeoning interest in health, health care reform and the advent of the Information Age, represents a challenge and an opportunity for public health. If public health's effectiveness and profile are to grow, practitioners and researchers will need reliable, timely information with which to make information-driven decisions, better ways to communicate, and improved tools to analyze and present new knowledge. "Public Health Informatics" (PHI) is the science of applying Information-Age technology to serve the specialized needs of public health. In this paper we define Public Health Informatics, outline specific benefits that may accrue from its widespread application, and discuss why and how an academic discipline of public health informatics should be developed. Finally, we make specific recommendations for actions that government and academia can take to assure that public health professionals have the systems, tools, and training to use PHI to advance the mission of public health.