Formerly known as the Celtic League, the Magners League is a 10-team competition involving regional teams from Ireland, Scotland and Wales.

The League runs from September to May and is used by the home unions to determine Heineken Cup qualification and seedings.

The championship is based solely on a traditional league format, but from the 2009-10 season the title will be decided via a play-off system similar to the English Premiership.

Two Italian teams will join the League from the 2010-11 season after organisers agreed in principle to extend the League if certain criteria were met.

The League's origins stem back to 1999, when Wales and Scotland created the Welsh-Scottish League.

In 2001 the Irish Rugby Football Union joined forces with Scotland and Wales to create a new competition which would involve the four Irish branches.

Fifteen teams competed in the League's inaugural season and were split into two groups for a series of round-robin matches, with the top four teams from each group qualifying for the knockout stages.

The Irish dominated the latter stages, with the final being contested between Munster and eventual champions Leinster.

In 2003 the Welsh regions were formed, which reduced the number of teams competing in the tournament, and the Celtic League became the sole professional tournament for the three countries, reverting to a traditional league format.

The League was renamed for the start of the 2006-07 season after Magners Irish Cider agreed a five-year sponsorship.