A flamethrower is a mechanical device designed to project a long controllable stream of fire.

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.