The widespread adoption of increasingly sophisticated forms of information technology has paralleled the increase in rapid and far-reaching international travel. The emergence and global spread of the 2009 pandemic influenza A (H1N1) virus illustrated not only the hazards of an interconnected world, but also the powerful role of new methods for detecting, tracking, and responding to infectious diseases. Although formal reporting, surveillance, and response structures remain essential to protecting public health, a new generation of freely accessible, online, and real-time informatics tools for disease tracking are expanding the ability of public health professionals to detect weak signals across borders and to raise earlier warnings of emerging disease threats.–