A National Special Security Event (NSSE) is an event of national or international significance deemed by the United States Department of Homeland Security (DHS) to be a potential target for terrorism or other criminal activity. These events have included summits of world leaders, meetings of international organizations, presidential nominating conventions and presidential inaugurations. NSSE designation requires federal agencies to provide full cooperation and support to ensure the safety and security of those participating in or otherwise attending the event, and the community within which the event takes place, and is typically limited to specific event sites for a specified time frame.

An NSSE places the United States Secret Service as the lead agency in charge of the planning, coordination, and implementation of security operations for the event, the Federal Bureau of Investigation in charge of intelligence, counterterrorism, and investigation of major criminal activities associated with the event, and the Federal Emergency Management Agency in charge of recovery management in the aftermath of terrorism, major criminal activities, natural disasters, or other catastrophic incidents following the event.