Responding to outbreaks is one of the most routine yet most important functions of a public health agency. However, some outbreaks are bigger, more visible, or more complex than others, prompting discussion about when an "outbreak" becomes a "public health emergency." When a public health emergency is identified, resources (eg, funding, staff, space) may need to be redirected from core public health programs to contribute to the public health emergency response. The need to sustain critical public health functions while preparing for public health emergency responses raises a series of operational and resource management questions, including when a public health emergency begins and ends, why additional resources are needed, how long an organization should expect staff to be redirected, and how many staff (or what proportion of the agency's staff ) an organization should anticipate will be needed to conduct a public health emergency response. This article addresses these questions from a national perspective by reviewing events for which the Centers for Disease Control and Prevention redirected staff from core public health functions to respond to a series of public health emergencies. We defined "public health emergency" in both operational and public health terms and found that on average each emergency response lasted approximately 4 months and used approximately 9.5% of our workforce. We also provide reasons why public health agencies should consider the impact of redirecting resources when preparing for public health emergencies.