A Molotov cocktail is a crude incendiary weapon which consists of a glass bottle filled with flammable liquid, usually gasoline (petrol) or alcohol (generally methanol or ethanol), and a rag stuffed in the mouth of the bottle. The weapon is used by lighting the rag and throwing the bottle at the target. The bottle shatters on impact, spilling the burning liquid over the target. Sometimes, if available, self-inflammatory materials (such as white phosphorus), could also be used to guarantee the bottle's explosion as it hits the target surface. Tar is often added to the composition in order to make the burning fluid stick to the target. Sometimes acid is added to the mix to increase the damaging potential of the liquid, and to increase the chances for it to penetrate fire-resistant surfaces. Molotov cocktails are easy to make and are the standard weaponry of guerrilla warfare and violent rioters.

The name "Molotov cocktail" is derived from Vyacheslav Molotov, who was the Foreign Minister and Secretary of War of the Soviet Union during World War II. The soldiers of the Finnish Army successfully used Molotov cocktails against Red Army tanks in the two conflicts (Winter War and Continuation War) between Finland and the Soviet Union and coined the term. Molotov cocktails were even mass-produced by the Finnish military, bundled with matches to light them. Petrol bombs had already been used in the Spanish Civil War, sometimes propelled by a sling.

These weapons saw widespread use by all sides in World War Two. They were very effective against light tanks, and very bad for enemy morale. The following is a first-hand description of their effects, written during the Warsaw Ghetto Uprising in 1943:

The well-aimed bottles hit the tank. The flames spread quickly. The blast of the explosion is heard. The machine stands motionless. The crew is burned alive. The other two tanks turn around and withdraw. The Germans who took cover behind them withdraw in panic. We take leave of them with a few well-aimed shots and grenades.
- Eyewitness Reporting for the Żydowska Organizacja Bojowa (Jewish Fighting Organization), 19 April, 1943