Get Inspired: RUGBY UNION
In the words of the Rugby Football Union (RFU), the sport is "a territorial, full-contact, team game, inclusive of all shapes and sizes, where 20-stone bulldozers are valued just as highly as small, pacey whippets".
Rugby union involves 15 players on each team, attempting to score tries at either end of the field by passing the ball between hands (but never forwards unless kicked).
Rugby sevens, a seven-a-side variant of the sport which has itself been played for more than a century, will make its Olympic debut at Rio 2016.
In England, the RFU website explains more about the various forms of rugby union, offers a club finder to help you locate a local team, and includes details of the women's game and how to get started.
The RFU's separate touch rugby website has an interactive map of nearby opportunities to try touch.
The Scottish Rugby Union's Get Involved website includes more information and a club finder.
Why is it good for you?
Playing rugby union is a fantastic sport for developing all-round fitness.
The skills and attributes you will benefit from depend on the position you play in. Forwards are typically stronger, heavier and entrusted with the more physical aspects of the game. Backs are relied upon for pace and agility.
Rugby sevens players have to cover a large field with fewer team-mates, so stamina and positioning become important qualities.
Union differs from rugby league in its use of rucks, mauls and scrums - various means of combining players from each side - to decide possession of the ball.
The invention of rugby union is famously credited to William Webb Ellis when, in 1823, he supposedly ran with the ball in his hands during a football match at Rugby School.
That story may or may not be true, but the game in the 21st Century is alive in thousands of teams up and down the United Kingdom.
The Rugby Football Union came into being in 1871, the same year as the sport's first international match, contested between England and Scotland. By the 1880s all four home nations were playing each other, and tours to Australia and New Zealand would take place before the century was out.
Rugby made four appearances at the Olympic Games, beginning with the 1900 Paris Games and including London 1908, Antwerp 1920 and a second Paris appearance in 1924.
The sport was subsequently dropped from the Olympic programme but rugby sevens has now won entry to the 2016 Rio Games, as well as being a staple of the Commonwealth Games.
Unlike rugby league, which split from union in the 1890s, rugby union remained amateur until 1995, following which the sport entered a new era with competitions like the Heineken Cup.