American League Division Series

In Major League Baseball, the American League Division Series (ALDS) determines which two teams from the American League will advance to the American League Championship Series. The Division Series consists of two best-of-five series, featuring each of the two division winners with the best records and the winners of the wild-card play-off.

History
The Division Series was implemented in 1981 as a one-off tournament because of a midseason strike, with the first place teams before the strike taking on the teams in first place after the strike. In 1981, a split-season format forced the first ever divisional playoff series, in which the New York Yankees won the Eastern Division series over the Milwaukee Brewers (who were in the American League until 1998) in five games while in the Western Division, the Oakland Athletics swept the Kansas City Royals (the only team with an overall losing record to ever make the postseason).

In 1994, it was returned permanently when Major League Baseball (MLB) restructured each league into three divisions, but with a different format than in 1981. Each of the division winners, along with one wild card team, qualify for the Division Series. Despite being planned for the 1994 season, the postseason was cancelled that year due to the 1994–95 Major League Baseball strike. In 1995, the first season to feature a division series, the Western Division champion Seattle Mariners defeated the wild card New York Yankees three games to two, while the Central Division champion Cleveland Indians defeated the Eastern Division champion Boston Red Sox in a three-game sweep.

From 1994 to 2011, the wild card was given to the team in the American League with the best overall record that was not a division champion. Beginning with the 2012 season, a second wild card team was added, and the two wild card teams play a single-game playoff to determine which team would play in the ALDS. For the 2020 Major League Baseball season only, there was an expanded playoff format, owing to an abbreviated 60-game regular season due to the COVID-19 pandemic. Eight teams qualified from the American League: the top two teams in each division plus the next two best records among the remaining teams. These eight teams played a best-of-three-game series to determine placement in the ALDS. The regular format returned for the 2021 season.

As of 2022, the Yankees have played in and won the most division series, with thirteen wins in twenty-two appearances. In 2015, the Toronto Blue Jays and Houston Astros were the final American League teams to make their first appearances in the ALDS. The Astros had been in the National League through 2012, and had played in the National League Division Series (NLDS) seven times. The Astros are the only team to win the ALDS in six consecutive seasons. The Yankees record of four consecutive victories was broken by the Astros with their victory in the 2021 ALDS against the Tampa Bay Rays.

Determining the matchups
The ALDS is a best-of-five series where the divisional winner with the best winning percentage in the regular season hosts the winner of the Wild Card Series between the top two wild card teams in one matchup, and the divisional winner with the second best winning percentage hosts the winner of the series between the lowest-seeded divisional winner and the lowest-seeded wild card team. (From 2012 to 2021, the wild card team was assigned to play the divisional winner with the best winning percentage in the regular season in one series, and the other two division winners met in the other series. From 1998 to 2011, if the wild-card team and the division winner with the best record were from the same division, the wild-card team played the division winner with the second-best record, and the remaining two division leaders played each other.) The two series winners move on to the best-of-seven ALCS. According to Nate Silver, the advent of this playoff series, and especially of the wild card, has caused teams to focus more on "getting to the playoffs" rather than "winning the pennant" as the primary goal of the regular season.

From 2012 to 2021, the wild card team that advances to the Division Series was to face the number 1 seed, regardless whether or not they are in the same division. The two series winners move on to the best-of-seven ALCS. Beginning with the 2022 season, the winner between the lowest-ranked division winner and lowest-ranked wild card team faces the number 2 seed division winner in the Division Series, while the 4 v. 5 wild card winner still faces the number 1 seed, as there is no reseeding even if the 6-seeded wild card advances. Home-field advantage goes to the team with the better regular season record (or head-to-head record if there is a tie between two or more teams), except for the wild-card team, which never receives the home field advantage.

Beginning in 2003, MLB has implemented a new rule to give the team from the league that wins the All-Star Game with the best regular season record a slightly greater advantage. In order to spread out the Division Series games for broadcast purposes, the two ALDS series follow one of two off-day schedules. Starting in 2007, after consulting the MLBPA, MLB has decided to allow the team with the best record in the league that wins the All-Star Game to choose whether to use the seven-day schedule (1-2-off-3-4-off-5) or the eight-day schedule (1-off-2-off-3-4-off-5). The team only gets to choose the schedule; the opponent is still determined by win–loss records.

Initially, the best-of-5 series played in a 2–3 format, with the first two games set at home for the lower seed team and the last three for the higher seed. Since 1998, the series has followed a 2–2–1 format, where the higher seed team plays at home in Games 1 and 2, the lower seed plays at home in Game 3 and Game 4 (if necessary), and if a Game 5 is needed, the teams return to the higher seed's field. When MLB added a second wild card team in 2012, the Division Series re-adopted the 2–3 format due to scheduling conflicts. However, it reverted to the 2–2–1 format starting the next season, 2013.

Years of appearance
In the sortable table below, teams are ordered first by number of wins, then by number of appearances, and finally by year of first appearance. In the "Season(s)" column, bold years indicate winning appearances.