If at great altitudes air is supplied to the carbureter of an engine at sea-level pressure, the power developed becomes approximately the same as when the engine is running at sea level. The low atmospheric pressure and density at great altitudes offer greatly reduced resistance to high airplane speeds; hence the same power that will drive a plane at a given speed at sea level will drive it much faster at great altitudes and with approximately the same consumption of fuel per horsepower-hour. Supercharging means forcing in a charge of greater volume than that normally drawn into the cylinders by the suction of the pistons. Superchargers usually take the form of a mechanical blower or pump and the various forms of supercharger are mentioned and commented upon. Questions regarding the best location for the carbureter in supercharged engines are then considered. Supercharging engines, in which compression in the crankease or in the lower end of the cylinders is used to force an additional volume of air or mixture into the cylinders after completion of their normal suction stroke, are then reviewed, with discussion of their special features and comments upon present practice. In conclusion, the future of the supercharger is considered and the chief obstacles which must be overcome are mentioned.