A bicycle chain is a chain that transfers power from the pedals to the drive-wheel of a bicycle thus propelling it.

The chain in use on all bicycles today is a roller chain with a 1/2" pitch and either a 1/8" or 3/32" width, the former being used on the common low cost coaster and three speed bicycles, and the latter being used on derailleur-equipped road, racing, and touring bicycles. Obsolete chain designs previously used on bicycles included the block chain , the skip-link chain , and the Simpson lever chain.

Before the safety bicycle, bicycles did not have chains and the pedals were attached directly to the drive-wheel, thus limiting top speed by the diameter of the wheel and resulting in very dangerous designs with front wheels as large as possible. Using chain drive allowed the mechanical advantage between the drive and driven sprockets to determine the maximum speed, thereby enabling manufacturers to reduce the size of the driving wheel for safety. It also allowed for the development of variable gearing, allowing cyclists to adjust their gearing to the difficulty of the terrain, on the fly.

Bicycle chains generally available today are made by:

• Campagnolo
• Shimano
• SRAM
• KMC