The United States, like all countries, faces many threats with the potential for large-scale health consequences, including disease outbreaks, natural disasters, and terrorist attacks. Preparing for and responding to these and other threats requires the commitment of, and co-operation among, all segments of society: government, the private sector, local communities, and international partners. This book presents the Nation's first National Health Security Strategy (NHSS), and Implementation Plan, which is intended to help galvanise efforts to minimise the health consequences associated with significant health incidents. The NHSS was developed in consultation with a broad range of stakeholders, including representatives from local, state, territorial, tribal, and federal government; community-based organisations; private-sector firms; and academia. The vision for health security described in the NHSS is built on a foundation of community resilience -- healthy individuals, families, and communities with access to health care and with the knowledge and resources to know what to do to care for themselves and others in both routine and emergency situations. Communities help build resilience by implementing policies and practices to ensure the conditions under which people can be healthy, by assuring access to medical care, building social cohesion, supporting healthy behaviours, and creating a culture of preparedness in which bystander response to emergencies is not the exception but the norm. Securing our Nation's health is a formidable task and must be a responsibility that is broadly shared among virtually all segments of society.