During certain emergencies (naturally caused or deliberate) that can have a significant impact on the public's health, the Secretary of the U.S. Department of Health and Human Services (HHS) has broad discretion to declare a Public Health Emergency (PHE). While many public health emergencies will not require a formal declaration, this type of declaration can be an important and necessary step to authorize the secretary to take a variety of actions that enable the department to respond optimally to an emergency. This article outlines the HHS Secretary's PHE authority, discusses possible discretionary actions that the secretary may take after declaring a PHE, and provides examples of PHE declarations that have been issued.