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 four divisions. Divisions 1A and 1B (ten teams in each) are played in the traditional double round-robin format with Divisions 2A and 2B (sixteen teams in each) played in a single round-robin format. At the end of the season, the bottom two teams in Divisions 1A and 1B are relegated and replaced by the top two teams from Divisions 1B and 2A respectively, and the bottom three teams in Division 2A are replaced by the top three from Division 2B. The two teams finishing bottom of Division 2B 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.