A flamethrower is a ranged incendiary device designed to project a controllable jet of fire. First deployed by the Byzantine Empire in the 7th century AD, flamethrowers saw use in modern times during World War I, and more widely in World War II as a tactical weapon against fortifications.

Most military flamethrowers use liquid fuel, typically either gasoline or diesel, but commercial flamethrowers are generally blowtorches using gaseous fuels such as propane; gases are safer in peacetime applications, because their flames have less mass flow rate and dissipate faster, and often are easier to extinguish when necessary.

The military use of flamethrowers is restricted through the Protocol on Incendiary Weapons.

Apart from the military applications, flamethrowers have peacetime applications where there is a need for controlled burning, such as in sugarcane harvesting and other land-management tasks. Various forms are designed for an operator to carry, while others are mounted on vehicles.