Professional racing originated in Western Europe, centred in France, Spain, Italy and the Low Countries. Since the mid-1980s, the sport has diversified, with professional races now held on all continents of the globe. Semi-professional and amateur races are also held in many countries. The sport is governed by the Union Cycliste Internationale (UCI). As well as the UCI's annual World Championships for men and women, the biggest event is the Tour de France, a three-week race that can attract over 500,000 roadside supporters a day.