The tactics and strategy of a guerrilla army. Nearly always politically motivated, guerrilla warfare is the art of harassing a larger, stronger, and (often) better trained professional military force with sabotage, subterfuge, and constantly shifting targets and angles of attack. It can be enormously effective against traditional military strategy, but it requires the support of the noncombatant native population, as well as tremendous leadership qualities across the entire guerrilla operation.

     Method of fighting used by the Viet Cong that was a protocol for survival rather than victory. Best suited for the jungle, Guerrilla warfare called for the placement of booby traps and the use of sneak attacks to damage the enemy critically while minimizing losses. This style of fighting was not meant for victory, but rather as an alternative to be being massacred in head to head combat. If the guerrillas could slowly demoralize the enemy, then victory could ultimately be achieved, no matter what the losses. Guerrillas fought to the death; there was no other alternative.

Much of modern guerrilla warfare is attributed to Che Guevara, who formed his vision of the strategy and the tactics required during the leadup to the Cuban Revolution. This does not mean to imply that Che invented the concept; many of the tenets of guerrilla resistance or insurgency are to be found, fully formed, in such ancient texts as Master Sun Tzu's The Art of War or Miyamoto Musashi's The Five Rings.

One minor quibble with yaar's writeup above concerning Vietnam's American War - while the strategy of guerrilla warfare was indeed one of survival for the Viet Cong, it should not be contrasted with a strategy for victory - the two were one and the same. As Ho Chi Minh is credited with saying, "to defeat the American we must cling to his belt buckle." The close-in fighting and concealment weren't just to avoid destruction, but to neutralize the American advantages in technology, materièl and firepower.

Guerrilla warfare is an increasingly common form of warfare in the modern era.

Due to the invention of nuclear weapons, the face of war changed dramatically after World War II. Because of the destructive potential of these new weapons, it was imperative that war did not escalate to a point where nuclear weapons became involved. This split warfare into 3 categories: nuclear warfare, conventional warfare, and guerrilla warfare.

While conventional warfare is usually between two different states, guerrilla warfare is more commonly intra-state conflicts associated with civil war. Guerrillas most commonly are fighting against the established forces of the government, and use hit and run tactics, unlike the army under the government's control, which will more likely use conventional tactics. The chief advantages of guerilla warfare are mobility and elusiveness. Since you never field any solid military units, the standing army has nothing to direct itself against.

Guerrilla warfare is dependant upon the common people for it's supplies of food, money, and recruits, and is typically only successful if they have popular support. While they may have their arms supplied by a third party nation, and even heavy weapons and monetary aid, the third party usually does not contribute troops.

Examples of modern day guerrilla wars:
Vietnam War
Malaya
Afghanistan
Algeria
Cyprus
The Cuban Revolution