The Pro12 (known as the Guinness Pro12 for sponsorship reasons) (formerly known as the Celtic League, Magners League and RaboDirect Pro12) is an annual rugby union competition involving twelve professional sides from Ireland, Italy, Scotland and Wales. The league is one of the three major professional leagues in Europe (along with the English Premiership and the French Top 14) the most successful teams from which go forward to compete in the European Rugby Champions Cup, the pan European championship which replaced the Heineken Cup after the 2013–14 season.
Beginning in the 2001–02 season, the league was originally known as the Celtic League (Irish: An tSraith Cheilteach; Italian: La Lega Celtica; Scots Gaelic: An Lìog Cheilteach; Welsh: Y Gynghrair Geltaidd) and comprised teams from Ireland, Scotland and Wales. The league was sponsored by Irish cider makers Magners from the 2006–07 season until 2010–11. At the start of the 2010–11 season, the league expanded from ten to twelve teams, adding two Italian teams and following the end of Magners sponsorship the league was sponsored by RaboDirect from 2011–12 through to 2013–14. The "Pro12" was adopted to reflect that it now includes teams from outside the Celtic nations. The current sponsorship deal with Guinness commenced at the beginning of the 2014–15 season.
The 2008–09 Celtic League (known as the 2008–09 Magners League for sponsorship reasons) was the eighth Celtic League season and the third with Magners as title sponsor. The season began in September 2008 and ended in May 2009. Ten teams played each other on a home-and-away basis, with teams earning four points for a win, and a bonus point for scoring four or more tries in a match. Losing teams also earned a bonus point if they lost by seven points or less.
The ten competing teams consisted of the four Irish provinces, Munster, Leinster, Connacht and Ulster; two Scottish regions, Edinburgh Rugby and Glasgow Warriors; and four Welsh regions, Cardiff Blues, Newport Gwent Dragons, Ospreys and Scarlets. The Scarlets were originally known as the "Llanelli Scarlets", but renamed themselves at the start of the season, in order to reflect their regional identity.
Munster were crowned champions on 30 April 2009 after the Ospreys beat the Newport Gwent Dragons 27–18 but failed to claim a bonus point.
The 2006–07 Celtic League (known as the 2006–07 Magners League for sponsorship reasons) was the sixth Celtic League season and the first with Magners as title sponsor. The season commenced on 1 September and was completed on 12 May.
The teams competing remained the same as the previous season with four Irish provinces; Munster, Leinster, Connacht and 2005–06 champions Ulster, three Scottish regions; Edinburgh, Border Reivers and Glasgow Warriors and four Welsh regions; Llanelli Scarlets, Cardiff Blues, Ospreys and Newport Gwent Dragons.
The league was won for the second time in three seasons by the Ospreys, with a final-day win over the Borders, playing their last ever match, as the Scottish Rugby Union have announced that the Borders will not exist next season
Ulster began the season as the reigning champions whilst Munster are Heineken Cup champions of the 2005–06 season. Prior to the season commencing it was announced by the Irish Rugby Football Union that some of their internationals were to be rested during part of the season as the Rugby World Cup takes place at the end. This would include the first four matches of the season, to allow for recovery from the June internationals. Those who did not play much during the internationals may return sooner. Major signings during the off-season include Justin Marshall for the Ospreys and Stephen Jones for the Scarlets. The free weekend scheme, where each team that did not compete in a match on a weekend due to the odd number of teams in the league would receive 4 points, was scrapped.