Cycling is an activity most commonly performed on a bicycle - when it is it is also referred to as bicycling or simply biking. It is the use of the bicycle, unicycle (unicycling), tricycles (tricycling), quadracycles (quadracycling), and other similar wheeled human-powered vehicles (HPVs) for the purpose of transport, as a form of recreation, or in racing. It is done on roads and paths, across open country or even over snow and ice (icebiking).

Bicycles were introduced in the 19th century and now number about one billion worldwide. They are the principal means of transportation in many regions.