Interleague play in Major League Baseball refers to regular-season baseball games played between an American League (AL) team and a National League (NL) team. Interleague play was first introduced in the 1997 Major League Baseball season. Prior to that, matchups between AL teams and NL teams occurred only during spring training, the All-Star Game, other exhibition games (such as the Hall of Fame Game in Cooperstown, New York), and the World Series. Unlike modern interleague play, none of these contests, except for the World Series, counted toward official team or league records.
Regular season interleague play was discussed for baseball's major leagues as early as 1903, when the two major leagues made peace and formed the National Commission as governing body. The first National Commission Chairman, Cincinnati president August Herrmann (who had already been a proponent of interleague play), proposed an ambitious scheme in late 1904. Herrmann's plan would have seen the two leagues ending their seasons earlier, after approximately 116 games, "and then have every National League team play two games in every American League city, and have every American League team play two games in every National League city."   Another interleague play idea was floated around the same time by Boston Americans owner John Taylor, whose plan was for each league to play its full 154-game schedule, to be followed by not just a championship series between the two league winners, but also by series' between the two second-place finishers, the two third-place teams, and all other corresponding finishers. 
In August 1933, several owners reacted favorably to a proposal by Chicago Cubs president William Veeck to have teams play four interleague games in the middle of the season, beginning in 1934.  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. 
MLB's first regular-season interleague game took place on June 12, 1997, as the Texas Rangers hosted the San Francisco Giants at The Ballpark in Arlington. There were four interleague games on the schedule that night, but the other three were played on the West Coast, so the Giants–Rangers matchup started a few hours earlier than the others. Texas's Darren Oliver threw the game's first pitch and San Francisco outfielder Glenallen Hill was the first designated hitter used in a regular-season game by a National League team. San Francisco's Darryl Hamilton got the first base hit in interleague play, while Stan Javier hit the first home run, leading the Giants to a 4–3 victory over the Rangers.
From 1997 to 2001, teams played against the same division from the other league; for example, the American League West played teams from the National League West, typically scheduled to alternate between home and away in consecutive years. In 2002, however, the league began alternating which divisions played which divisions, and thus in 2002 the American League East played the National League West, the American League Central played the National League East, and the American League West played the National League Central. Matchups which had been of particular interest prior to this format — mainly geographic rivals — were preserved. This is expected to be the continuing format of the interleague schedule. Corresponding divisions were skipped once when this rotation began, but were put back in the rotation in 2006.
From 2002 to 2012, all interleague games were played prior to the All-Star Game (with the exception of games postponed by weather that were made up after the All-Star Game). Most games were played in June and early July, although beginning in 2005, interleague games were played during one weekend in mid-May.
The designated hitter (DH) rule is applied in the same manner as in the World Series (and the All-Star Game prior to 2010). In an American League ballpark, both teams have the option to use a DH. In a National League ballpark, both teams' pitchers must bat. Teams from both leagues have both benefited and have been at a disadvantage when it comes to the DH rule in interleague play. For instance, Barry Bonds, who spent his entire career in the National League and actually won eight Gold Gloves earlier in his career, was used strictly as a DH later in his career when the San Francisco Giants played away interleague games due to his poor fielding.  Conversely, Boston Red Sox slugger David Ortiz, who spent his entire career in the American League and was the Red Sox's regular DH, was forced to play first base when the Red Sox had away interleague games, forcing the Sox to give up good defensive fielding in favor of retaining Ortiz's power hitting. 
In 2007, two teams — the Los Angeles Dodgers and the Baltimore Orioles — played six games with more than one interleague opponent. The Dodgers played both the Toronto Blue Jays and the Los Angeles Angels while the Orioles played both the Arizona Diamondbacks and the Washington Nationals. This happened again in 2012 as the New York Yankees played both the New York Mets and the Atlanta Braves for six games. The Miami Marlins also did this, playing both the Tampa Bay Rays and Boston Red Sox for six games each. Unless major changes are made to the current interleague format, this will not happen again.
The first Civil Rights Game was an exhibition interleague game between the Cleveland Indians and St. Louis Cardinals at AutoZone Park in Memphis on March 31, 2007. The first regular season Civil Rights Game was an interleague game between the Chicago White Sox and Cincinnati Reds at Great American Ball Park on June 20, 2009.
Since the introduction of interleague play, two teams have shifted leagues: the Milwaukee Brewers from the American League to the National League in 1998, and the Houston Astros from the National League to the American League in 2013. As a result, a 2013 interleague series between the two teams made it the first time that two teams faced each other in an interleague series after both teams previously faced each other in an interleague series representing opposite leagues: the two teams met from September 1–3, 1997 (Houston in NL, Milwaukee in AL), then again from June 18–20, 2013 (Houston in AL, Milwaukee in NL). In both instances, the series took place in Houston, with the team representing the American League winning 2–1.   From 1998 to 2012, both teams were division opponents in the National League Central.
For the 2020 season, all interleague games will feature the DH, as the National League will use the rule for the first time in its history due to the COVID-19 pandemic. 
Interleague play has largely favored the American League in terms of win-loss records. In 22 years of play, the AL has won the season series 17 times, including 14 straight from 2004 to 2017.
As of the end of the 2018 MLB season, the American League holds an all-time series advantage of 3,032–2,732 and has finished with the better record in interleague play for 14 straight seasons, dating back to 2004 until 2018.  2006 was the most lopsided season in interleague history, with American League teams posting a 154–98 record against their National League counterparts.  The team with the best all-time record in interleague play is the New York Yankees of the AL at 144–102 (.585), followed by the Chicago White Sox at 143–104 (.579). The Miami Marlins holds the NL's best interleague record at 127–107 (.543), followed by the St. Louis Cardinals at 109–96 (.532). 
With the Pirates sweeping the Royals on September 19, 2018, the National League guaranteed the series win for the first time since 2003. 
|Year||Best record||Total games||American League||National League||Winning pct.*||Notes|
The following is the 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." 
Certain interleague matchups are highly anticipated each year, due to the geographic proximity of the teams involved. Many cities, metropolitan areas and states contain at least one team in each league. In each of these "natural rivalry" matchups, the two teams meet annually for four games, two in each ballpark. Prior to 2013, and in 2015 and 2018, there were six games between the two teams, three per ballpark:
- Baltimore Orioles v. Washington Nationals — Beltway Series, MASN Cup, Battle of the Beltways, Parkway Series, or MARC Madness.  Introduced in 2006, the Nationals′ second season in Washington, D.C., after their move from Montreal.
- Chicago Cubs v. Chicago White Sox — Windy City Series, Crosstown Classic or Red Line Series. The two teams played in the 1906 World Series.
- Cincinnati Reds v. Cleveland Indians — Ohio Cup
- Detroit Tigers v. Pittsburgh Pirates — While this series only became a rivalry because the other AL and NL Central teams were already paired up, it has become popular with fans of both teams, possibly due to the rivalry between the NHL's Detroit Red Wings and Pittsburgh Penguins. The two teams have several other connections as well. The Tigers' AA Minor League affiliate, the Erie SeaWolves, located near Pittsburgh, is a former affiliate of the Buccos, and has retained the logo of a wolf wearing a pirate bandanna and eye patch. Additionally, Jim Leyland, former manager of both the Pirates (1986–1996) and the Tigers (2005–2013), remains popular in Pittsburgh where he continues to reside. The two teams played in the 1909 World Series.
- Kansas City Royals v. St. Louis Cardinals — I-70 Series or Show-Me Series, and named so because the cities of Kansas City and St. Louis are both in Missouri, and connected by Interstate 70. The two teams played in the 1985 World Series.
- Los Angeles Angels v. Los Angeles Dodgers — Freeway Series
- Miami Marlins v. Tampa Bay Rays — Citrus Series
- Milwaukee Brewers v. Minnesota Twins —Border Series The Twins and the Brewers were formerly regional rivals in the American League, as well as division rivals from 1970 to 1971, and again from 1994 to 1997. The two metro areas are connected by Interstate 94. However, the term "I-94 Series" is used almost exclusively to refer to the games played between the Milwaukee Brewers and the Chicago Cubs, and interleague contests with the also-former-rival Chicago White Sox.
- New York Mets v. New York Yankees — Subway Series The two teams played in the 2000 World Series. The addition of the Mets in 1962 brought National League baseball back to New York after the Dodgers and Giants moved to California in 1958.
- Oakland Athletics v. San Francisco Giants — Bay Bridge Series or Battle of the Bay. The two teams played in the 1989 World Series as well as the 1905 World Series, 1911 World Series, and 1913 World Series when they were located in Philadelphia and New York, respectively.
- San Diego Padres v. Seattle Mariners - Originally played as they were the only west-coast teams not to be paired up with another interleague rival. The two teams share a Spring Training complex in Peoria, Arizona. Often cited as a counterargument against "rivalry" series in general due to the teams' lack of a historical rivalry and their locations on opposite ends of the Pacific Coast (and the I-5 corridor), as well as both teams' general underachievement throughout their time as "rivals." Sometimes jokingly referred to as the Vedder Cup after Pearl Jam singer Eddie Vedder, who has lived in both cities (although Vedder himself, raised in the Chicago area, is a Chicago Cubs fan). 
In 2014, the ten teams that qualified for the postseason were five pairs of geographical rivals: the Angels, Athletics, Orioles, Royals, and Tigers from the AL; and Dodgers, Giants, Nationals, Cardinals, and Pirates from the NL.
Four teams in the East and West form a "split rivalry" where the rivalry pairings alternate in odd- and even-numbered years.
In the East:
- Odd-numbered years:
- Even-numbered years:
- Boston Red Sox v. Atlanta Braves (the Braves played in Boston as the Boston Red Stockings, Red Caps, Beaneaters, Doves, Rustlers, and Braves from 1871 through 1952)
- Toronto Blue Jays v. Philadelphia Phillies (These two teams played in the 1993 World Series, where Joe Carter hit a walk-off home run during Game 6)
In the West:
- Odd-numbered years:
- Even-numbered years:
In years in which the AL East plays the NL East and the AL West plays the NL West (2015, 2018, etc.), the teams play their assigned "rival" for the year six times and the other "rival" either three or four times.
- Baltimore Orioles v. Philadelphia Phillies – Played from 1997 to 2005. In 2006, the Washington Nationals replaced the Phillies as the Orioles' rival. Although the Nationals moved to Washington in 2005, the schedule for that season was already established, so the Washington-Baltimore rivalry series could not start until the next season. Therefore, in 2005 the Orioles played the Phillies as their rival for the last time, while Washington played Montreal's planned 2005 schedule, which included what would have been the Expos's interleague rivalry games with the Toronto Blue Jays.
- Houston Astros v. Texas Rangers ( Lone Star Series) – Played from 2001 to 2012. In 2013, the Astros moved to the American League West, and the two teams began play against each other 19 times a year as divisional rivals.
- Arizona Diamondbacks v. Texas Rangers – Played from 1998 to 2000 when the Diamondbacks were an expansion team. Revived in 2013 and 2015 as part of a split rivalry with the Rockies and Astros.
- Montreal Expos v. Toronto Blue Jays ( Pearson Cup or The All-Canadian Series) – Played from 1997 to 2004 (and by Washington against Toronto in 2005). By the time the Expos moved to Washington, D.C., to become the Washington Nationals for the 2005 season, the 2005 schedule already had been set, so the Nationals played what had been intended as Montreal's rivalry series with the Blue Jays that season. In 2006, the Nationals began playing the Baltimore Orioles annually as their interleague rival.
1997 was the first year of regular season interleague play. The 20 teams in the east and central divisions played 15 games each in five three-game series. The eight teams in the west divisions played 16 games each in eight two-game series, playing home and away two-game series against each team.
1998 had the MLB add the Devil Rays and Diamondbacks as expansion teams. All the teams in the American League played 16 games, playing one four-game series (split into two home, two away) and four three-game series and the National League played games from a range between 12 and 16 games, depending on the team.
From 1999 through 2012, each team in the American League played 18 interleague games a year, but because the National League had two more teams than the American, only four NL teams would play a full 18-game interleague schedule, with the remaining twelve teams plying only 15. With the exception of the two NL teams playing each other, all teams were involved in interleague play at the same time (originally in June and July), playing only interleague opponents until the interleague schedule was complete for the year. The schedule was later changed to occur only in June; in 2005, it was changed again to allow for more weekend interleague games, with each team playing one series during the third weekend in May and the rest in mid-to-late June (occasionally stretching into early July).
In 2013, the Houston Astros joined the American League, giving each league 15 teams and thereby necessitating that interleague games be played throughout the season, including on Opening Day and during key division races all the way to the end of the season. This did not require expanding the total number of interleague games, because the probability of an interleague game during the era in which the Astros played in the NL was 252/2430 or about 1 in 9.6 games (this number is not an integer because not all teams had the same number of interleague games). With an odd number of teams in each league, one team in each league would be the "odd man out" and have to play an interleague game to fill out the schedule, meaning as few as 1 in 15 games could be interleague (14 AL teams in 7 AL games, 14 NL teams in 7 NL games and 1 AL and 1 NL team in an interleague game). Despite this, there have been proposals to increase interleague play to 30 games.  While the increase to 30 games is highly unlikely for the foreseeable future, a smaller increase took place immediately, having every team play 20 interleague games. 
Since the 2013 season, the 20 interleague games are played in eight series. Each team plays one three-game series against four teams from one division in the other league, and two two-game series (one home, one away) against the remaining team in that division. Divisions have been rotated since 2002 but teams did not necessarily play everyone in that division prior to 2013. The remaining four games are played against a team's "natural rival" in home and home two-game series. From 2013 to 2017 these two series were back-to-back at one venue on Monday and Tuesday and at the other team's venue that Wednesday and Thursday. Should a team's natural rival be a member of the division they are scheduled to play as part of the yearly rotation (this first occurred for all teams in 2015), the team will play home-and-home three game series against the natural rival, home-and-home two game series against two other opponents, and single three game series against the last two (one home, one away). For 2013, all natural rivalry games were played May 27–30. Teams played at one park on May 27 and 28, then traveled to the other team's park for games on May 29 and 30. For 2014, 2016, and 2017, these games were spread out throughout the season, ranging from the second week of the season in April through mid-August. Because the requirement for nearly daily interleague play (the only exception being if not all teams are playing) spreads out interleague play throughout the year, not every team will be in interleague play on the same day. Due to the new CBA lengthening the schedule by four days, 2018 was the first year during which no team was required to play back-to-back home-and-home two game series against any other team.
In 2020 due to the COVID-19 pandemic the schedule was shortened from 162 games to 60 and interleague opponents were switched to the corresponding divisions. The teams played 20 interleague games using the same format that is normally used when corresponding teams played each other (six games against a rival and three or four against the other teams in that division).
Most days, there will be either one or three interleague games as the average number of interleague games per day will be 1.68 [(20 interleague games per team x 30 teams in MLB)/(183 total days in baseball season, including off days, but excluding the All-Star break)/2 teams per game]. With 15 teams in each league, the number of interleague games is almost always odd, with exceptions based on when teams from each of the AL and NL have the same off day. Doubleheaders and make-up games also apply should a rainout or other extended delay requires one or more games to be postponed.
On April 1, 2013, for the first time in major league baseball history, an interleague game was played on Opening Day, between the Los Angeles Angels of Anaheim and the Cincinnati Reds at Great American Ball Park, with the Angels claiming the distinction of winning that game, 3–1, in 13 innings. The Reds, however, would win the next two contests by scores of 5–4.  Also, on September 29, 2013, for the first time in major league baseball history, an interleague game was played on the last day of the regular season, between the Miami Marlins and the Detroit Tigers at Marlins Park. The Marlins not only claimed the distinction of winning that game, 1–0, in walk-off fashion, but also saw their pitcher Henderson Álvarez pitch a no-hitter, marking just the 7th time a no-hitter was tossed in an interleague contest.
On April 3, 2016, for the first time in MLB history, the previous year's World Series participants faced off on Opening Day the following year. The Kansas City Royals hosted the New York Mets at Kauffman Stadium in a nationally televised game and won, 4–3. The Mets would not only return the favor two days later with a 2–0 win to split the two game series, but also sweep two more from the Royals in Citi Field on June 21–22 that year.
With the Pittsburgh Pirates' victory over the Oakland Athletics on July 10, 2013, every team has beaten every other team at least once; the A's had previously been 11–0 all time against the Pirates.  
Every team has also hosted and visited every other team at least once. This distinction was completed in July 2016 when the San Diego Padres made their first trip to Toronto. The two teams had previously played in San Diego in 2004, 2010, and 2013.
During 1997–2001, the divisions were paired with their geographical counterpart (AL East vs. NL East, AL Central vs. NL Central, AL West vs. NL West). Beginning in 2002, the divisional pairings rotated. The geographical counterparts were initially skipped in 2004, but returned to the schedule in 2006, creating a three-year rotation that remains in use. In 2020, due to the COVID-19 pandemic, the originally scheduled matchups were adjusted in order to limit travel. Divisional pairings for recent and upcoming seasons are:
|Season||NL East vs.||NL Central vs.||NL West vs.||AL East vs.||AL Central vs.||AL West vs.|
|2017||AL West||AL East||AL Central||NL Central||NL West||NL East|
|2018||AL East||AL Central||AL West||NL East||NL Central||NL West|
|2019||AL Central||AL West||AL East||NL West||NL East||NL Central|
|2020 [note 1]||AL East||AL Central||AL West||NL East||NL Central||NL West|
|2021||AL East||AL Central||AL West||NL East||NL Central||NL West|
- The 2020 season was originally slated to have AL East vs NL Central, AL Central vs NL West, and AL West vs NL East. However, this was changed to have each division play its geographical counterpart in order to reduce travel in a shortened season due to the COVID-19 pandemic.
Since its introduction, regular-season interleague play has continued to be a source of controversy among baseball fans and others involved with the sport. Among the arguments used in favor of and in opposition to interleague play are the following:
- Interleague matchplay increases attendance; however, these numbers may be skewed, as interleague games were previously primarily played on weekends, when attendance is higher across the board, and were played in June, when school is not in session and temperatures are higher than some of the other months of the season.  However, season-long interleague play should mitigate this statistical bias.
- Fans can see players they might not otherwise get to see, especially those who have only ever played in one league.
- Certain geographic rivalries are played out during the regular season that otherwise might not happen for years at a time. The Yankees now play four or six games against the Mets each season (depending on the divisional alignment of interleague play each season) whereas they would only have gone head to head in the 2000 World Series if not for interleague play. From 1962 until interleague play, the Mets and the Yankees had only played each other in the Mayor's Trophy Game (held from 1963 to 1983), which was an exhibition game even though it was played during the regular season.
- It creates matchups that might not have been seen in generations. For example:
- During the 2004 season, the Giants and Red Sox played each other for the first time since meeting in the 1912 World Series.
- The Red Sox had never played at Wrigley Field (an NL park since 1916) until 2005. Conversely, the Chicago Cubs' trip to Fenway Park in 2011 was their first appearance there since the teams met in the 1918 World Series. The Cubs played their home games in that series in the more expansive Comiskey Park.
- In 2004, the Yankees and Dodgers met for the first time since the 1981 World Series at Dodger Stadium. They didn't meet at the Bronx until 2013, making the Dodgers the only team to never have played a regular season game at the old Yankee Stadium.
- In 2008, the New York Yankees visited the Pittsburgh Pirates for the first time since the 1960 World Series.
- It allows for a rematch of the previous World Series. This has occurred in 13 of the 23 completed seasons of interleague play. Despite this, the World Series winning team has only won the season series four of these times. The most notable example of this is in 2016 when the New York Mets and Kansas City Royals, who met in the 2015 World Series, met again on Opening Day in Kansas City.
- It allows the relative strength of the two leagues to be measured against each other over 300 games per year, rather than just in the World Series once per year.
- Most American League pitchers do not like taking batting practice for the opportunity to bat in one or two games (unless they've played in the National League before.) These pitchers are also unaccustomed to running the bases, which can lead to injury and premature fatigue. (For example, Chien-Ming Wang of the New York Yankees suffered a season-ending lisfranc sprain on his right foot when running the bases during an interleague game against the Houston Astros in 2008.)
- The World Series and All-Star Game are robbed of the mystique that used to result from the two leagues playing completely exclusive schedules during the regular season: in the case of the World Series, the "best in the American League" playing the "best in the National League" for the only time that season.
- More games against interleague opponents means fewer games against same-league and division rivals – the latter of which may be more compelling. However, the leagues currently play an unbalanced schedule that favors divisional opponents rather than teams from other divisions (which is important due to the postseason qualifying structure – only the best team from a given division is guaranteed a berth in the postseason). Now, divisional opponents meet each other 19 times per season, and each natural rivalry sees only 4 games as opposed to 6 in previous years (except when playing the division of the natural rival).
- Some have argued that the AL possesses an unfair advantage over the NL because of the designated hitter rule in the AL, citing the overwhelming dominance of the AL in interleague play for more than a decade. When NL teams are on the road, they are forced to find a DH in place of their pitcher, who would normally bat ninth. Sometimes, the NL team will use one of their star hitters as the DH and use a bench player to fill in for the appointed DH, and other times, the NL team will simply use a bench player as the DH and have him bat later. In either case, however, the benefits of using a DH in place of the pitcher are minimal, especially considering that the AL designated hitters have seen more action in their positions and that AL teams still possess their full 9-man batting lineup. Even when the NL team is hosting, arguments have been made that there is no real benefit for the NL team either. For the most part, designated hitters are also passable fielders, meaning that they can still be used in the game. And even though the AL team has to take a player out of their lineup, it leaves them with a starting player available to pinch-hit and/or come in as a substitute player later in the game, as opposed to a bench player on an NL team. And although AL pitchers see less action than NL pitchers, stats have showed that AL pitcher batting average is not much lower than NL pitcher batting average, in large part due to the fact that several AL pitchers have played in the NL. For these reasons, some have argued that the NL should adopt the DH, while others have argued that the AL should drop the DH.
- These cons applied primarily to the 1997–2001 and/or 2002–2012 formats and not necessarily to the current format:
- The "rivalry" series that consist of six games a year for some teams leads to further scheduling inequities. For example, the AL West race can be skewed by Seattle getting six games per year against last-place San Diego and Oakland's six matchups against defending champion San Francisco.
- Some teams play a certain inter-league team more than a certain intra-league team. For example, the Washington Nationals played the Baltimore Orioles (an AL team) 6 times in the 2012 season, and the San Diego Padres and Pittsburgh Pirates (NL teams) only 5 times each. This will no longer be the case starting 2013, when every pair of intra-league foes are guaranteed six meetings against each other, three at each venue.
- Most notably, teams no longer play identical opponents as their divisional rivals, and even where they do, they don't always play them an identical number of times. This can lead to "
strength of schedule" disparities like those the
NFL has to deal with on a yearly basis.
- For example, in 2005, the San Diego Padres played every AL Central team except for Kansas City, who had the worst record in the league, as well as six games against Seattle, who finished that season 69–93.
- Meanwhile, their division rivals, the San Francisco Giants, played every AL Central team except for the Chicago White Sox, who had the best record in the AL and went on to win the World Series, in addition to six against Oakland, who was in playoff contention for most of the season.
- In the current format these inequities are sharply reduced, since all teams within a division will have the same opponents from the rotating division each season, while the rivalry series is reduced to four games each season (except when playing each other's division).
- "Herrmann's Plan Is Quite Unique". 1904-11-17 – via Pittsburgh Press.
- "Herrmann's Plans for Post-Season Games". 1904-12-01 – via Pittsburgh Press.
- "Herrmann's Plan Is Quite Unique". Pittsburgh Press. 1904-11-17.
- Drebinger, John (1956-12-06). "Player limit, Interleague Games Top Issues on Majors' Agenda". New York Times. Retrieved 2009-10-02.
- Hurwitz, Hy (1963-05-04). "Veeck Predicts Big Time Will Adopt Interloop Play". The Sporting News. p. 4.
- Koppett, Leonard (1976-02-18). "Drastic Changes Seen For Baseball". New York Times. Retrieved 2011-10-01.
- "Baseball Approves Interleague Play". New York Times. January 19, 1996. Retrieved 2011-10-01.
- "Who should sign Barry Bonds?". Hardballtimes.com. 2008-03-04. Retrieved 2013-02-28.
- "Red Sox's David Ortiz ready to take the field in interleague play – MLB – Sporting News". Aol.sportingnews.com. 2012-05-18. Retrieved 2013-02-28.
- "1997 Houston Astros Schedule, Box Scores and Splits". Baseball-Reference.com. Retrieved 2013-07-22.
- "2013 Houston Astros Schedule, Box Scores and Splits". Baseball-Reference.com. Retrieved 2013-07-22.
- "New rules in place for 2020 season". MLB.com. Retrieved 2020-07-23.
- "Interleague History: All-Time Club Records in Interleague Play". MLB.com. Major League Baseball. 2010-06-28. Retrieved 2010-06-28.
- "NL ends AL's 14-year Interleague win streak". MLB. Retrieved 2018-09-20.
- Interleague History (MLB.com/News/Awards/History/Interleague/Home). MLB Advanced Media, L.P. Retrieved 2009-08-31.
- "Nats or Orioles? In Washington, some families are a hardball house divided". Washington Post. Retrieved 30 September 2014.
- Young, Geoff (2012-06-12). "Western Front: A Brief History of the Vedder Cup". Baseball Prospectus. Retrieved 11 January 2018.
- "Increase in Interleague games unlikely in 2013 | MLB.com: News". Mlb.mlb.com. Retrieved 2013-02-28.
- "MLB's 2013 interleague schedule is a huge step in the right direction - ESPN". Espn.go.com. 2012-05-19. Retrieved 2013-02-28.
- "Reds use three homers to beat Angels". St. Louis Post Dispatch. April 5, 2013. Retrieved April 6, 2013.
- "Oakland Athletics vs. Pittsburgh Pirates - Gameflash - July 10, 2013". Sports Illustrated. Retrieved 2013-07-22.
- "Oakland Athletics vs. Pittsburgh Pirates - Recap - July 08, 2013 - ESPN". Scores.espn.go.com. 2013-07-08. Retrieved 2013-07-22.
- The Enid News and Eagle, Enid, OK – Rivalies add to interleague play
- A game scheduled between the Milwaukee Brewers and the Minnesota Twins in Milwaukee was cancelled and not made up.
- A game scheduled between the Florida Marlins and the New York Yankees in New York was cancelled and not made up.
- A 3-game series between the Philadelphia Phillies and the Toronto Blue Jays scheduled for Toronto was moved to Philadelphia with the Designated Hitter (DH) rule in effect due to the G20 summit.
- A 3-game series between the Florida Marlins and the Seattle Mariners scheduled for Florida was moved to Seattle with the Designated Hitter (DH) rule not in effect due to scheduling conflicts with the U2 360° Tour.
- Several games were relocated due to the COVID-19 outbreak and 2 games between the Tigers and Cardinals in Detroit were canceled and not made up.
- Proposals for interleague play prior to 1997 at the Wayback Machine (archived September 28, 2007)
- For head to head listings, choose team and the time period to get full list and results