The Britannica Encyclopaedia describes a motorcycle as a bicycle or tricycle propelled by an internal-combustion engine (or, less often, by an electric engine).

The motors on minibikes, scooters, and mopeds, or motorized velocipedes, are usually air-cooled and range from 25 to 250 cubic cm (1.5 to 15 cubic inches) in displacement; the multiple-cylinder motorcycles have displacements of more than 1,300 cubic cm.

The automobile was the reply to the 19th-century dream of self-propelling the horse-drawn carriage. Similarly, the invention of the motorcycle created the self-propelled bicycle. The first commercial design was a three-wheeler built by Edward Butler in Great Britain in 1884. This employed a horizontal single-cylinder gasoline engine mounted between two steerable front wheels and connected by a drive chain to the rear wheel.

The 1900s saw the conversion of many bicycles, or pedal cycles by adding small, centrally mounted spark ignition engines. There was then felt the need for reliable constructions. This led to road trial tests and competition between manufacturers. Tourist Trophy (TT) races were held on the Isle of Man in 1907 as reliability or endurance races. Such were the proving ground for many new ideas from early two-stroke-cycle designs to supercharged, multivalve engines mounted on aerodynamic, carbon-fibre reinforced bodywork.