Rugby union is both a professional and amateur game, and is dominated by the first tier unions: Argentina, Australia, England, France, Ireland, Italy, New Zealand, Scotland, South Africa and Wales. Second and third tier unions include Brazil, Canada, Chile, Colombia, Fiji, Georgia, Japan, Mexico, Namibia, Peru, Portugal, Romania, Russia, Samoa, Spain, Tonga, United States, Uruguay and Venezuela. Rugby Union is administered by the International Rugby Board (IRB), whose headquarters are located in Dublin, Ireland. It is the national sport in New Zealand, South Africa, Wales, Fiji, Samoa, Tonga and Madagascar, and is the most popular form of rugby globally, with the seven-a-side version of the game, known as Rugby sevens, having been admitted into the program of the Olympic Games from Rio de Janeiro in 2016 onwards.
In Canada and the United States, rugby union evolved into gridiron football. During the late 1800s (and even the early 1900s), the two forms of the game were very similar (to the point where the United States was able to win the gold medal for rugby union at the 1924 Summer Olympics), but numerous rule changes have differentiated the gridiron-based game from its rugby counterpart.