The United States Army Special Forces, colloquially known as the "Green Berets" due to their distinctive service headgear, are a special operations force of the United States Army that are designed to deploy and execute 9 doctrinal missions: unconventional warfare, foreign internal defense, direct action, counter-insurgency, special reconnaissance, counter-terrorism, information operations, counterproliferation of weapons of mass destruction, and security force assistance. The first two missions, unconventional warfare and foreign internal defenses emphasize language, cultural, and training skills in working with foreign troops. Other Special Forces missions, known as secondary missions, include: combat search and rescue (CSAR), counter-narcotics, hostage rescue, humanitarian assistance, humanitarian demining, information operations, peacekeeping, and manhunts. Other components of the United States Special Operations Command (USSOCOM) or other U.S. government activities may also specialize in these secondary missions. The Special Forces conduct these missions via seven geographically focused groups. Many of their operational techniques are classified, but some nonfiction works and doctrinal manuals are available.
As special operations units, Special Forces are not necessarily under the command authority of the ground commanders in those countries. Instead, while in theater, SF units may report directly to a geographic combatant command, USSOCOM, or other command authorities. The Central Intelligence Agency's (CIA) highly secretive Special Activities Center (formerly known as the "Special Activities Division") and more specifically its Special Operations Group (SOG) recruits from the U.S. Army's Special Forces. Joint CIA–Army Special Forces operations go back to the MACV-SOG branch during the Vietnam War. The cooperation still exists today and is seen in the War in Afghanistan.