The Defense Advanced Research Projects Agency (DARPA) is an agency of the United States Department of Defense responsible for the development of new technology for use by the military. DARPA has been responsible for funding the development of many technologies which have had a major impact on the world, including computer networking, as well as NLS, which was both the first hypertext system, and an important precursor to the contemporary ubiquitous graphical user interface.

Its original name was simply Advanced Research Projects Agency (ARPA), but it was renamed DARPA (for Defense) on 23 March 1972, then back to ARPA on 22 February 1993, and then back to DARPA again on 11 March 1996.

DARPA was established in 1958 in response to the Soviet launching of Sputnik in 1957, with the mission of keeping U.S. military technology ahead of the nation's enemies. From DARPA's own introductionBridging the Gap:

DARPA's original mission, established in 1958, was to prevent technological surprise like the launch of Sputnik, which signaled that the Soviets had beaten the U.S. into space. The mission statement has evolved over time. Today, DARPA's mission is still to prevent technological surprise to the US, but also to create technological surprise for our enemies.

DARPA is independent from other more conventional military R&D and reports directly to senior Department of Defense management. DARPA has around 240 personnel (about 140 technical) directly managing a $3.2 billion budget. These figures are "on average" since DARPA focuses on short-term (two to four-year) projects run by small, purpose-built teams.

DARPA's mission

DARPA's own introduction:

DARPA is a Defense Agency with a unique role within DoD. DARPA is not tied to a specific operational mission: DARPA supplies technological options for the entire Department, and is designed to be the “technological engine” for transforming DoD.

Near-term needs and requirements generally drive the Army, Navy, Marine Corps, and Air Force to focus on those needs at the expense of major change. Consequently, a large organization like DoD needs a place like DARPA whose only charter is radical innovation.

DARPA looks beyond today's known needs and requirements. As military historian John Chambers noted, “None of the most important weapons transforming warfare in the 20th century – the airplane, tank, radar, jet engine, helicopter, electronic computer, not even the atomic bomb – owed its initial development to a doctrinal requirement or request of the military.” None of them. And to this list, DARPA would add unmanned systems, Global Positioning System (GPS) and Internet technologies.