The league is the second highest level of rugby union in Ireland, as professional teams representing the four provinces of Ireland play in the Pro12.
Division 1 sides are allowed to field only two professional players in their matchday sides, and only one may be a forward. Professional players may not participate in Division 2 matches. Foreign professional players may not play in the League.
The All-Ireland League has been dominated by teams from Limerick who have won 13 out of 23 titles. Teams from Munster have won 17 out of 23. The All-Ireland League was not sponsored in the initial season, but was sponsored for six years by Insurance Corporation of Ireland. The League was sponsored by Allied Irish Banks from 1998 to 2010.Ulster Bank has sponsored the league since 2010.
The league is divided into five divisions of ten teams each, with teams playing each other twice (once at home and once away). At the end of the season, the top four teams in Division 1A play off semi-finals and a final for the championship and the bottom team in Divisions 1A is replaced by the top team in Division 1B, with the second-bottom team entering a promotion/relegation play-off with the second-placed team in 1B. The bottom two teams in 1B, 2A and 2B are relegated and replaced by the top two teams from Divisions 2A, 2B and 2C respectively. The two teams finishing bottom of Division 2C are relegated to the relevant provincial league and replaced by the two teams finishing top of a "round robin" tournament between the four provincial league winners. The four provincial junior leagues are the Connacht Junior League, the Leinster League, the Munster Junior League and the Ulster Qualifying League.