Cyclocross (or cyclo-cross) is a form of bicycle racing. Races take place typically in the autumn and winter (the international season is September-January), and consists of many laps of a short (2-3km) course featuring pavement, wooded trails, grass, steep hills, and obstacles requiring the rider to dismount, jump the barrier and remount. Races for senior categories are generally between 50 minutes and an hour long, with the distance varying depending on the ground conditions. The sport is administered by the Union Cycliste Internationale; it began in the 1940s and the first world championship was held in Paris in 1950. The sport is strongest in the traditional road cycling countries (and particularly so in Flanders).
Cyclo-cross has some obvious parallels with cross-country mountain bicycle racing and many of the best cyclo-cross riders are also stars of mountain biking. But cyclo-cross bicycles are similar to racing bicycles: lightweight, with narrow tyres. They have to be lightweight because competitors need to carry their bicycle to overcome barriers or slopes too steep to climb in the saddle. The sight of competitors struggling up a muddy slope with bicycles on their shoulders is the classic image of the sport, although unridable sections are generally a very small fraction of the race distance.
Compared with other forms of cycle racing, tactics are fairly straightforward, and the emphasis is on the rider's aerobic endurance and bike-handling skills.
A cyclo-cross rider is allowed to change bicycles and receive mechanical assistance during a race. While the rider is on the course gumming up one bicycle with mud, their pit crew can work quickly to clean, repair and oil the spares.
