Rapidly providing a definitive diagnostic test that can be used broadly by healthcare providers and members of the public in the setting of a disease emergency is critical to limit pathogen spread, develop and deploy medical countermeasures, and mitigate the social and economic harms of a serious epidemic or pandemic. There is extraordinary expertise within and outside of government working on these issues, and major accomplishments have been made to accelerate test development, expand laboratory testing capacity, and establish widespread point-of-care testing. Still, the United States does not have a plan to rapidly respond, to develop, manufacture, or deploy at national scale diagnostic testing in the earliest days of a new infectious disease crisis. Nor does the nation have a plan to sustain testing capacity at high volume over the course ofan enduring epidemic or pandemic. To address this gap, we are proposing a National Diagnostics Action Plan that describes the steps that are urgently needed to prepare for future infectious disease emergencies, as well as the actions we must take at the first signs of such events. These recommendations require substantial collaboration between the US government (USG) and the private sector to solve a series of challenges now, as well as to prepare for the massive and rapid scale-up of laboratory and point-of-care test development and testing capacity in future emergencies. The recommendations include establishing pre-event contracts; ensuring rapid access to clinical samples; creating a permanent public-private testing coordinating body to allow for rapid information sharing and improved cooperation among the USG, test developers, and clinical laboratories; and accelerating testing rollout at the beginning of an event—andthus, the effective public health management of a disease crisis. These recommendations were informed by extensive discussion with people who managed the COVID-19 and monkeypox responses, review of past reports written on diagnostic challenges, and the experiences of the authors.