History
Also known as the International Championship, this rugby tournament originated with a challenge match between England and Wales in 1882. It quickly became the Four Nations Tournament, as Scotland and Ireland got involved.
In the early years, the participants frequently squabbled about the tournament rules and format. Three times, in 1885, 1887, and 1889, the tournament couldn't be finished because of unresolved disputes. And England didn't compete in 1888 because the country refused to join the new International Rugby Football Board.
France joined the competition in 1910, making it the Five Nations Tournament, but the French team was forced to withdraw in 1931 because its player were being paid by their clubs and therefore could no longer be considered amateurs. France was readmitted in 1947. In 2000, Italy was also added to the mix, creating the Six Nations Tournament.
Because the tournament uses a round-robin format, with each team playing one match against each other team, there hasn't always been a clear-cut champion. In fact, there was a five-way tie in 1973 because each country won two matches and lost two. There have also been several three-way ties for the championship.
Since 1994, cumulative and comparative scores have been used to break ties.
Incidentally, the phrases "Triple Crown" and "Grand Slam" entered sports terminology because of this tournament. When one of the United Kingdom teams beats the other three, it has won the Triple Crown. When one of the five nations won all four of its tournament matches, it was referred to as the Grand Slam. Presumably, the phrase (which originally came from contract bridge) will now be applied to the feat of winning all five matches in the Six Nations Tournament.