A bicycle is a human-powered vehicle consisting of two wheels aligned in tandem, connected by a frame. It is propelled by pedaling, which turns a chain-driven mechanism attached to the rear wheel. Most bicycles include handlebars for steering, a saddle for seating, and a braking system for speed control.

Modern bicycles evolved during the 19th century and have since become one of the most common forms of transportation worldwide. Designs vary depending on purpose, including road bicycles for speed and paved surfaces, mountain bikes for off-road terrain, and hybrid models for general commuting.

Bicycles are valued for their efficiency, low cost, and minimal environmental impact. They require no fuel other than human energy and produce no direct emissions. In addition to transportation, bicycles are widely used for recreation, sport, and fitness. Their simplicity and adaptability make them an important component of sustainable urban mobility systems around the world.