Keirin (競輪 / ケイリン, [keːɾiɴ]) – literally "racing cycle" – is a form of motor-paced cycle racing in which track cyclists sprint for victory following a speed-controlled start behind a motorized or non-motorized pacer. It was developed in Japan around 1948 for gambling purposes and became an official event at the 2000 Olympics in Sydney, Australia.

Riders use brakeless fixed-gear bicycles. Races are typically 1.5 kilometres (0.93 mi) long: 6 laps on a 250 m (270 yd) track, 4 laps on a 333 m (364 yd) track, or 4 laps on a 400 m (440 yd) track. Lots are drawn to determine starting positions for the sprint riders behind the pacer, which is usually a motorcycle, but can be a derny, electric bicycle or tandem bicycle. Riders must remain behind the pacer for 3 laps on a 250 m (270 yd) track. The pacer starts at 30 km/h (19 mph), gradually increasing to 50 km/h (31 mph) by its final circuit. The pacer leaves the track 750 m (820 yd) before the end of the race (3 laps on a 250 m (270 yd) track). The winner's finishing speed can exceed 70 km/h (43 mph).

Competition keirin races are conducted over several rounds with one final. Some eliminated cyclists can try again in the repechages.