A flamethrower is a mechanical incendiary device designed to project a long, controllable stream of fire. They were first used by the Greeks in the 1st Century AD. In modern times, they were used during World War I, and more widely in World War II.

Some flamethrowers project a stream of ignited flammable liquid; some project a long gas flame. Most military flamethrowers use liquids, but commercial flamethrowers tend to use high-pressure propane and natural gas, which is considered safer. They are used by the military and by people needing controlled burning capacity, such as in agriculture (e.g., sugar cane plantations) or other such land management tasks. They can be designed to be either carried by the operator or mounted on a vehicle.