Invented by Robert Goddard (1882-1945), a liquid-fuel rocket mixes a fuel and an oxidizer in a combustion chamber (sometimes with the help of an igniter), and disperses the exhaust products of the exothermic reaction through a nozzle, producing thrust due to Newton's Third Law. Goddard launched the first liquid-fuel rocket on March 16, 1926, from his Aunt Effie's farm. The flight lasted 2 and a half seconds; the rocket achieved a top speed of 60 mph (just shy of 110 kmh), a maximum altitude of 41 feet, and travelled downrange 184 feet.

Because liquid fuels can be stored separately from their oxidizers, they safely store much more chemical energy than the same mass of any stable solid fuel. Common rocket fuels include just about any flammable liquid. Common oxidizers are most nitric acids (esp. IRFNA) and of course, liquid oxygen. Goddard's first rockets used gasoline for fuel and liquid oxygen as the oxidizer. It may prove educational for Americans to read about Sergei Pavlovich Korolev and Wernher von Braun, to get an idea of how much of liquid-fuel rocket technology came from Russia.