1st Special Forces Operational Detachment-Delta (1st SFOD-D), popularly known as Delta Force, is one of the United States' four secretive tier-one counter-terrorism and Special Mission Units. It was formerly listed as the Combat Applications Group by the Department of Defense but has since been officially re-designated the Army Compartmented Elements (ACE). While 1st SFOD-D is administratively supported by USASOC, it falls under the operational control of the Joint Special Operations Command. Delta Force and its Navy counterpart, the Naval Special Warfare Development Group, are the United States military's primary counter-terrorism units.

Delta Force's primary tasks are counter-terrorism, direct action, and national intervention operations, although it is an extremely versatile group capable of conducting many types of covert missions, including, but not limited to, hostage rescues and raids.

The Central Intelligence Agency's highly secretive Special Activities Division (SAD) and more specifically its elite Special Operations Group (SOG) often works with – and recruits – operators from Delta Force.