Each September, the United States observes National Preparedness Month, a month dedicated to raising awareness of public health preparedness. Preparedness—a field that readies our nation to respond to a range of emergencies—is a newer public health discipline, advanced by lessons learned from each response to a public health threat. While significant progress has been made over the past 20 years, the COVID-19 pandemic has shed light on the need to strengthen state and local capabilities to address future emergencies. The history of public health preparedness is worth understanding, as each current and future response is impacted by lessons from the past.