The Electronic Surveillance System for the Early Notification of Community-Based Epidemics (ESSENCE) was developed by the Johns Hopkins University Applied Physics Laboratory (JHU/APL) in collaboration with the Maryland Department of Health and Mental Hygiene, the District of Columbia Department of Health, and the Virginia Department of Health under the sponsorship of the Defense Advanced Research Projects Agency (DARPA). It is now used in the Department of Defense Global Emerging Infections System (DoD-GEIS). It is currently deployed in the National Capital Area (NCA) (Lombardo et al., 2004). The system monitors both military and civilian healthcare data daily for early outbreak detection and warning, fusing information from multiple data sources that vary in their medical specificity, spatial organization, scale, and time-series behavior (Burkom et al., 2004). ESSENCE has gone through a series of important development stages, and its most current prototype is ESSENCE IV. Figure 10-1 shows the system architecture of ESSENCE. It collects public health status information from three major channels: clinical data, nonclinical syndromic data, and health events-related information. The accessibility of the collected information is managed by either disclosure control or sharing polices to ensure the privacy of personal healthcare information. Automated outbreak detection and alerting are supported. Situation and threat awareness and epidemiology investigation support are integrated with secured Web-based visualization and user interfaces.