Rugby union (often referred to as just rugby, or union) is a variant of rugby football. Rugby union is normally played by teams with 15 players, although there is also rugby sevens, a quicker game with 7 players a side. The name comes from the name of the game's original governing body, the Rugby Football Union. It is one of the two codes of rugby, the other being rugby league.

Like other forms of rugby football the game was developed from the rules used to play football at Rugby school in England. The crucial differences from football (soccer) are that in rugby the ball is a prolate spheroid instead of a sphere and that the players are allowed to pick the ball up and run with it. The players are also allowed to throw the ball from player to player, but unlike American football they are not allowed to throw it forwards, it must only go sideways or backwards.

Rugby union was founded in England, in 1823. It has established itself as the national sport in New Zealand, Fiji, Tonga and Samoa, and is a popular sport in England, Wales, Ireland, Scotland, France, Australia, Argentina and South Africa. Rugby is also gaining popularity in Italy and Japan, following Italy's acceptance into the Six Nations and Japan's unsuccessful bid to host 2011 Rugby World Cup, which will be hosted in New Zealand.

The International Rugby Board (IRB), founded in 1886, governs the sport and also publishes the game's laws. There are currently 95 full members and 8 associate member countries. According to IRB figures, rugby is being played in over 100 countries spanning five continents by men and women of all ages. The IRB controls the Rugby World Cup, the Women's Rugby World Cup, Rugby World Cup Sevens, IRB World Sevens Series, Under 21 World Cup, Under 19 World Championship, and the Super Powers Cup. It will hold votes to decide where these events shall be held.