The rainbow jersey is the distinctive jersey worn by the reigning world champion in a cycling discipline, since 1927. The jersey is predominantly white with five horizontal bands in the UCI colours around the chest. From the bottom up the colours are: green, yellow, black, red and blue; the same colours that appear in the rings on the Olympic flag. The tradition is applied to all disciplines, including road racing, track racing, cyclo-cross, BMX, Trials and the disciplines within mountain biking. A world champion must wear the jersey when competing in the same discipline, category and speciality for which the title was won. For example, the world road race champion would wear the garment while competing in stage races and one-day races, but would not be entitled to wear it during time trials. Similarly, on the track, the world individual pursuit champion would only wear the jersey when competing in other individual pursuit events. In team events, such as the team pursuit, each member of the team must wear the rainbow jersey, but would not wear it while racing in, say, points races or other track disciplines. If the holder of a rainbow jersey becomes leader of a stage race or a category within it, that leadership jersey takes precedence. Failure to wear the rainbow jersey where required carries a penalty of a fine.

The Union Cycliste Internationale is the world governing body for sports cycling and oversees international competitive cycling events. The UCI is based in Aigle, Switzerland.