Public health surveillance is the systematic, ongoing assessment of the health of a community, and it is crucial to public health practice. Surveillance provides the information base for public health decision making. There is a constant need for new, updated information, as well as constantly changing priorities within the community. In the past, no single resource has been available to supply a guide to the underlying principles and practice of surveillance. This text fills that gap, providing an organized approach to planning, developing, and implementing public health surveillance systems. It will provide the public health professional and the student of epidemiology in any environment with the theoretical and practical tools necessary to create and implement effective surveillance programs.