Rugby union, commonly known simply as rugby, is a close-contact team sport that originated at Rugby School in the first half of the 19th century. Rugby is simply based on running with the ball in hand. In its most common form, a game is played between two teams of 15 players each, using an oval-shaped ball on a rectangular field called a pitch. The field has H-shaped goalposts at both ends.

Rugby union is a popular sport around the world, played by people of all genders, ages and sizes. In 2014, there were more than 6 million people playing worldwide, of whom 2.36 million were registered players. World Rugby, previously called the International Rugby Football Board (IRFB) and the International Rugby Board (IRB), has been the governing body for rugby union since 1886, and currently has 101 countries as full members and 18 associate members.

In 1845, the first laws were written by students attending Rugby School; other significant events in the early development of rugby include the decision by Blackheath F.C. to leave The Football Association in 1863 and, in 1895, the split between rugby union and rugby league. Historically rugby union was an amateur sport, but in 1995 formal restrictions on payments to players were removed, making the game openly professional at the highest level for the first time.

Rugby union spread from the Home Nations of Great Britain and Ireland, with other early exponents of the sport including Australia, New Zealand, South Africa and France. The sport is followed primarily in the British Isles, France, Georgia, Oceania, Southern Africa, Argentina, and to a lesser extent Italy, Uruguay, the United States, Canada, and Japan, its growth occurring during the expansion of the British Empire and through French proponents (Rugby Europe) in Europe. Countries that have adopted rugby union as their de facto national sport include Fiji, Georgia, Madagascar, New Zealand, Samoa, Tonga, and Wales.

International matches have taken place since 1871 when the first game was played between Scotland and England at Raeburn Place in Edinburgh. The Rugby World Cup, first held in 1987, is held every four years. The Six Nations Championship in Europe and The Rugby Championship in the Southern Hemisphere are other important international competitions that are held annually.

National club and provincial competitions include the Premiership in England, the Top 14 in France, the Bunnings NPC in New Zealand, the League One in Japan and the Currie Cup in South Africa. Other transnational club competitions include the United Rugby Championship of club teams from Ireland, Italy, Scotland, South Africa and Wales, European Rugby Champions Cup in Europe, and Super Rugby Pacific in Australia, New Zealand and the Pacific Islands.