Interleague or interconference matchups have long been the norm in other professional sports leagues such as the NFL. Regular season Interleague Play was discussed for baseball's major leagues as early as the 1930s. In December 1956, Major League owners considered a proposal by Cleveland general manager and minority owner Hank Greenberg to implement limited Interleague Play beginning in 1958. Under Greenberg's proposal, each team would continue to play a 154-game season, with 126 within that team's league, and 28 against the eight clubs in the other league. The interleague games would be played immediately following the All-Star Game. Notably, under Greenberg's proposal, all results would count in regular season game standings and league statistics. While this proposal was not adopted, the current system shares many elements. Bill Veeck predicted in 1963 that Major League Baseball would someday have Interleague Play. While the concept was again considered in the 1970s, it was not implemented until the 1990s, at least in part as an effort to renew the public's interest in MLB following the 1994 players' strike.
For the first time in Major League Baseball history, teams from the American League and National League competed in regular season, head-to-head competition during the 1997 season. The first Interleague game was on June 12, 1997 as the Texas Rangers hosted the San Francisco Giants at The Ballpark in Arlington.For the first five seasons of Interleague Play, each division played against the same division from the other league (NL East vs. AL East, NL Central vs. AL Central and NL West vs. AL West). As of the 2002 season, a new format to Interleague Play was instituted where teams play Interleague games against various divisions.
During Interleague Play the designated hitter rule is used in all American League ballparks, but is not used in National League stadiums, which is how the DH is used in World Series play. From 1997-99, umpire crews for each Interleague game came from the league where the game was being played. Starting in 2000, MLB has used common umpires for all games.
The following is text of Major League Baseball's policy regarding the compilation of statistics as a result of Interleague Play:
For the first time in the history of Major League Baseball, Interleague games are to be played during the regular season. Breaking tradition always brings about controversy and the matter of baseball records is no exception.
It is the opinion of Major League Baseball that there is no justification for compiling a new volume of records based on Interleague Play. On the contrary, the sovereignty of each league's records will be retained, and if a player or a team breaks a record against an Interleague opponent it will be considered a record in that league. In cases where two teams -- as Interleague opponents -- break a league or Major League record, that record will be annotated with the phrase 'Interleague game.' Streaks by both teams and individual will continue (or be halted) when playing Interleague opponents in the same manner as if playing against an intraleague opponent. In essence, records will be defined by who made them rather than against whom they were made.
The official statistics of both leagues will be kept separately as they have in the past. This means statistics for each team and their individual players will reflect their performance in games within the league and also in Interleague games without differentiation.
| Year | Best Record | American League | National League |
| 1997 | National | 97 | 117 |
| 1998 | American | 114 | 110 |
| 1999 | National | 116 | 135 |
| 2000 | American | 136 | 115 |
| 2001 | American | 132 | 120 |
| 2002 | National | 123 | 129 |
| 2003 | National | 115 | 137 |
| 2004 | American | 127 | 125 |
| 2005 | American | 136 | 116 |
| 2006 | American | 154 | 98 |
| 2007 | American | 137 | 115 |
| 2008 | American | 149 | 103 |
| 2009 | American | 138 | 114 |
| 2010 | American | 134 | 118 |
| 2011 | American | 131 | 121 |
| 2012 | American | 142 | 110 |
| 2013 | American | 154 | 136 |
| 2014 | American | 163 | 137 |
| 2015 | American | 167 | 133 |
| 2016 | American | 165 | 135 |
| 2017 | American | 160 | 140 |
| 2018 | National | 158 | 142 |
| 2019 | National | 166 | 134 |
| 2020 | Tie | 149 | 149 |
| 2021 | American | 167 | 133 |
| 2022 | American | 152 | 148 |
| Overall | American | 3,516 | 3,211 |
NOTE:
The Milwaukee Brewers played in the AL from 1997-1998
The Houston Astros played in the NL from 1997-2012
