The Centers for Disease Control and Prevention (CDC) WONDER is an online database for epidemiologic research. The database utilizes a rich ad-hoc query system for the analysis of public health data. Reports and other query systems are available to public health professionals and the public at large. The database provides access to a wide array of public health information. It allows free access to statistical research data published by CDC, as well as reference materials, reports and guidelines on health-related topics including public-use data sets about mortality (deaths), cancer incidence, HIV and AIDS, tuberculosis, vaccinations, natality (births), census data and many other topics. CDC Wonder is valuable in public health research, decision making, priority setting, program evaluation, and resource allocation.