The Six Nations Championship is an annual international rugby union competition between the teams of England, France, Ireland, Italy, Scotland and Wales. It is the oldest sports tournament contested by the Home Nations. The championship holders are Ireland, who won the 2024 tournament.

The tournament is organised by the unions of the six participating nations under the banner of Six Nations Rugby, which is responsible for the promotion and operation of the men's, women's and under-20s tournaments, and the Autumn International Series, as well as the negotiation and management of their centralised commercial rights.

The Six Nations is the successor to the Home Nations Championship, played between teams from England, Ireland, Scotland, and Wales, which was the first international rugby union tournament. With the addition of France, this became the Five Nations Championship, which in turn became the Six Nations Championship with the addition of Italy in 2000.

England and Wales have won the championship the most times, both with 39 titles, but England have won the most outright titles with 29. Since the Six Nations era started in 2000, only Italy and Scotland have failed to win the Six Nations title.

The women's tournament started as the Women's Home Nations in the 1996 season. The men's Six Nations Under 20s Championship is the successor to the Under 21s tournament which began in 2004.