A bicycle, also known as a bike, pushbike or cycle, is a pedal-driven, human-powered, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist or a bicyclist. Bicycles were introduced in the 19th century and now number about one billion worldwide, twice as many as automobiles. They are the principal means of transportation in many regions. They also provide a popular form of recreation, and have been adapted for such uses as children's toys, adult fitness, military and police applications, courier services and bicycle racing. The basic shape and configuration of a typical upright bicycle has changed little since the first chain-driven model was developed around 1885. However, many details have been improved, especially since the advent of modern materials and computer-aided design. These have allowed for a proliferation of specialized designs for particular types of cycling.
Wooden draisine (around 1820), the first two-wheeler and as such the archetype of the bicycle.

The great majority of today's bicycles have a frame with upright seating which looks much like the first chain-driven bike. Such upright bicycles almost always feature the diamond frame, a truss consisting of two triangles: the front triangle and the rear triangle. The front triangle consists of the head tube, top tube, down tube and seat tube. Being the first human means of transport to make use of the two-wheeler principle, the draizine (or Laufmaschine, "walking machine"), invented by the German Baron Karl von Drais, is regarded as the forerunner of the modern bicycle. It was introduced by Drais to the public in Mannheim in summer 1817 and in Paris in 1818. Its rider sat astride a wooden frame supported by two in-line wheels and pushed the vehicle along with his/her feet while steering the front wheel.