Conventional aircraft today are propelled by the action of propellers or jets, and powered by the internal combustion of petroleum fuels in piston, turboprop or jet engines. But other power sources, powerplants, and propulsion devices, for airships as well as aircraft, have been proposed and even experimented with over the last few centuries. The power sources considered include human muscles, steam, batteries, nuclear reactors, and hydrogen fuel; and the propulsion devices include sails, oars, flapping wings, rockets and cycloidal propellers. This meticulously researched book presents the history of these unconventional aerial power and propulsion systems, explains the underlying science and technology behind them, and assesses the crucial question of practicality.