Unconventional warfare (abbreviated UW) is the opposite of conventional warfare. Where conventional warfare is used to reduce the opponent's military capability, unconventional warfare is an attempt to achieve military victory through acquiescence, capitulation, or clandestine support for one side of an existing conflict.
On the surface, UW contrasts with conventional warfare in that forces or objectives are covert or not well-defined, tactics and weapons intensify environments of subversion or intimidation, and the general or long-term goals are coercive or subversive to a political body.
The general objective of unconventional warfare is to instill a belief that peace and security are not possible without compromise or concession. Specific objectives include inducement of war-weariness, curtailment of civilian standards of living and civil liberties associated with greater security demands, economic hardship linked to the costs of war; hopelessness to defend against assaults, terror, depression, and disintegration of morale. Two original definition are claiming: "The intent of U.S. Unconventional Warfare efforts is to exploit a hostile power’s political, military, economic, and psychological vulnerabilities by developing and sustaining resistance forces to accomplish U.S. strategic objectives." or according to John F. Kennedy: "There is another type of warfare—new in its intensity, ancient in its origin—war by guerrillas, subversives, insurgents, assassins; war by ambush instead of by combat, by infiltration instead of aggression, seeking victory by eroding and exhausting the enemy instead of engaging him. It preys on unrest. 
The ultimate goal of this type of warfare is to motivate an enemy to stop attacking or resisting even if it has the ability to continue. Failing this, a secondary objective can be to debilitate the enemy before a conventional attack.
Methods and organization
Unconventional warfare targets civilian population psychologically to win hearts and minds, and only targets military and political bodies directly, seeking to render the military proficiency of the enemy irrelevant. Limited conventional warfare tactics can be used unconventionally to demonstrate might and power, rather than to substantially reduce the enemy's ability to fight. In addition to the surgical application of traditional weapons, other armaments that specifically target military can be used are: nuclear weapons, incendiary devices, or other such weapons.
Special Forces, inserted deep behind enemy lines, are used unconventionally to train, equip, and advise locals who seek to change their oppressive regimes. They can also spread subversion and propaganda, while they aid native resistance fighters, to ultimately cause a hostile government to capitulate. Tactics focus on destroying military targets while avoiding damage to civilian infrastructure and blockading military resupply are used to decrease the morale of government forces.
The Department of Defense defines unconventional warfare as activities conducted to enable a resistance movement or insurgency to coerce, disrupt, or overthrow a government or occupying power by operating through or with an underground, auxiliary, and guerrilla force in a denied area. Also called UW. Source: JP 1-02, Department of Defense Dictionary of Military and Associated Terms
- Asymmetric warfare
- Hybrid warfare
- Fourth generation warfare
- Irregular military
- Irregular Warfare
- Low intensity conflict
- Partisan (military)
- Political Warfare
- Psychological warfare
- Resistance movement
- Unrestricted Warfare
- A seminal work on unconventional stay-behind warfare is Major Hans von Dach's Der Totale Widerstand (Total Resistance (book)).
US & NATO specific:
- United States Army, John F. Kennedy Special Warfare Center and School, Fort Bragg - Special Operations Forces- Unconventional Warfare, Training Circular No. 18-01, Oct. 2011
- Insurgency Research Group - Multi-expert blog dedicated to the study of insurgency and the development of counter-insurgency policy.
- Allied war terminology (File #5a)
- Unconventional Warfare: Definitions from 1950 to the Present[dead link]
- Unconventional Warfare: A Better Path to Regime Change in the Twenty First Century
- Instruments of Statecraft: U.S. Guerrilla Warfare, Counterinsurgency, and Counterterrorism, 1940-1990
- Pentagon plans cyber-insect army