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Prior to 1990, there was no national league in Ireland. Each of the four provincial unions had its own cup and league tournament. In 1991, after almost five years of discussion and consultation with clubs, the All-Ireland League (AIL) was introduced with two divisions, division 1 with 9 clubs and division 2 with 10 clubs. The AIL was expanded to four divisions in 1993–94, with small variations in the numbers of teams per division in subsequent seasons.

In 2000–01 the league was restructured to three divisions, each with 16 teams. After the 1995 introduction of professionalism in rugby union, the IRFU increased the importance of the provinces, which from 2002 participated in the Celtic League (now the United Rugby Championship) as full-time teams rather than ad hoc selections of club players. Therefore, the best Irish players no longer played in the AIL. In 2004 the IRFU proposed scrapping the All-Ireland League and reintroducing a provincial league system in 2005–06 which would act as qualifiers for a curtailed three division AIL structure in the second half of the season, but this model did not receive the support of clubs or rugby pundits. In 2007 the IRFU agreed that the structure of the All-Ireland League would remain as three divisions with 16 clubs each for seasons 2008–09 and 2009–10. In 2009–10, division 1 was split into 1A and 1B with eight teams in each as a trial and then continued in season 2010–11. In 2011–12 division 1A and 1B had 10 clubs each and divisions 2 and 3 were reformatted as divisions 2A and 2B with 16 clubs in each division.