Cork Constitution, the inaugural winners, are the only club to have retained top division status since the inception of the league.

[1] The League consists of 5 divisions of 10 teams each playing a double round-robin competition using the standard Rugby union bonus points system.

The season runs from mid-September until mid-April, with an approximately four-week break in matches from mid-December to early-January.

At the completion of the league phase the top 4 teams in Division 1A qualify for the play-off semi-finals, with the two winners meeting in the final.

[9] 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.

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.

[10][11] 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.