American League The American League of Professional Baseball Clubs , or simply the American League ( AL ) , is one of two leagues that make up Major League Baseball in the United States and Canada . It developed from the Western League , a minor league based in the Great Lakes states , which eventually aspired to major league status . It is often called the Junior Circuit because it claimed Major League status for the 1901 season , 25 years after the formation of the National League ( the " Senior Circuit " ) . At the end of every season , the American League champion plays in the World Series against the National League champion . Through 2012 , American League teams have won 62 of the 108 World Series played since 1903 , with 27 of those coming from the New York Yankees alone . The 2012 American League champions are the Detroit Tigers . The New York Yankees have won 40 American League titles , the most in the league ' s history , followed by the Philadelphia / Kansas City / Oakland Athletics ( 15 ) and the Boston Red Sox ( 12 ) . History . Originally a minor league known as the Western League , the league later developed into a major league after the American Association disbanded . In its early history , the Western League struggled until 1894 , when Ban Johnson became the president of the league . Johnson led the Western League into major league status and soon became the president of the newly renamed American League . Babe Ruth , noted as one of the most prolific hitters in Major League Baseball history , spent the majority of his career in the American League . The American League has one notable difference over the National League , in that since 1973 it has had the designated hitter rule . Under the rule , a team may use a batter in its lineup who is not in the field defensively , usually replacing the pitcher in the batting order , compared to the old rule that made it mandatory for the pitcher to hit . In 1977 , the league expanded to fourteen teams , when the Seattle Mariners and Toronto Blue Jays were enfranchised . Granting a team to Toronto marked the AL ' s expansion to Canada , following the National League ' s expansion to Montreal , and the Mariners were added in an attempt to settle a pending $ 90 million lawsuit against the league by the city of Seattle over the quick departure of the Seattle Pilots in 1970 . Until the late 1970s , league umpires working behind home plate wore large , balloon - style chest protectors worn outside the shirt or coat , while their brethren in the National League wore chest protectors inside the shirt or coat . In 1977 , new umpires ( including Steve Palermo ) had to wear the inside chest protector , although those on staff wearing the outside protector could continue to do so . Most umpires made the switch to the inside protector , led by Don Denkinger in 1975 and Jim Evans two years later , although several did not , including Bill Haller , Lou DiMuro , George Maloney and Jerry Neudecker , who became the last Major League umpire to use the outside protector in 1985 . In 1994 , the league , along with the National League , reorganized again , into three divisions ( East , West , and Central ) and added a third round to the playoffs in the form of the League Divisional Series , with the best second - place team advancing to the playoffs as a wild - card team , in addition to the three divisional champions . In 1998 , the newly franchised Tampa Bay Devil Rays joined the league , and the Arizona Diamondbacks joined the National League : i . e . , each league each added a fifteenth team . An odd number of teams per league meant that at least one team in each league would have to be idle on any given day , or alternatively that odd team out would have had to play an interleague game against its counterpart in the other league . The initial plan was to have 3 five - team divisions per league with interleague play year - round — possibly as many as 30 interleague games per team each year . For various reasons , it soon seemed more practical to have an even number of teams in both leagues . So , the Milwaukee Brewers agreed to change leagues , moving from the AL Central to the NL Central . ( This was the first time since the 1890s that a team had moved from one major league to another . ) At the same time , the Detroit Tigers shifted over to the AL Central , making room for the Devil Rays in the East . ) After the Houston Astros move to the AL West in 2013 , the leagues will once again each have 15 teams . For the first 96 years , American League teams faced their National League counterparts only in exhibition games or in the World Series . Beginning in 1997 , interleague games have been played during the regular season and count in the standings . As part of the agreement instituting interleague play , the designated - hitter rule is used only in games where the American League team is the home team . Through the 2012 season , the Yankees have won the most American League pennants ( 40 ) , followed by the Athletics ( 15 ) , Red Sox ( 12 ) , and Tigers ( 11 ) . Likewise , the Yankees have also won the most World Series ( 27 ) , with the Athletics second in the American League with nine , the Red Sox third with seven , and the Tigers fourth with four . Teams . Charter franchises . There were eight charter teams in 1901 , the league ' s first year as a major league , and the next year the original Milwaukee Brewers moved to St . Louis to become the St . Louis Browns . These franchises constituted the league for 52 seasons , until the Browns moved to Baltimore and took up the name Baltimore Orioles . All eight original franchises remain in the American League , although only four remain in the original cities ( Detroit , Chicago , Boston , and Cleveland ) . The eight original teams and their counterparts in the " Classic Eight " were : Current teams . American League West . ( * ) See commentary on Western League page . The Indianapolis and Minneapolis teams were replaced by teams in Baltimore and Philadelphia in 1901 , but it is unclear and disputed as to which team went where . Other leagues . Several other sports have had leagues called " American League , " usually with the sport name as a qualifier , such as the " American Football League " ( which eventually merged with the National Football League , adopting the latter ' s name for the combination ) . The American Hockey League is the top minor league in North American professional ice hockey .