Public health relies on data reported by health care partners, and information technology makes such reporting easier than ever. However, data are often structured according to a variety of different terminologies and formats, making data interfaces complex and costly. As one strategy to address these challenges, health information organizations (HIOs) have been established to allow secure, integrated sharing of clinical information among numerous stakeholders, including clinical partners and public health, through health information exchange (HIE). We give detailed descriptions of 11 typical cases in which HIOs can be used for public health purposes. We believe that HIOs, and HIE in general, can improve the efficiency and quality of public health reporting, facilitate public health investigation, improve emergency response, and enable public health to communicate information to the clinical community.