|League||Major League Baseball|
|Most recently played||2021|
|Defending champions||Atlanta Braves (4)|
|Most titles||New York Yankees (27)|
|Sponsor||YouTube TV (2017–2019)|
|Part of a series on the|
|Major League Baseball postseason|
|League Championship Series|
The World Series is the annual championship series of Major League Baseball (MLB) in the United States and Canada, contested since 1903 between the champion teams of the American League (AL) and the National League (NL). The winner of the World Series championship is determined through a best-of-seven playoff, and the winning team is awarded the Commissioner's Trophy. As the series is played during the fall season in North America, it is also referred to as the Fall Classic. From 2017 to 2019, the event was officially known as the World Series presented by YouTube TV for sponsorship reasons.
Prior to the AL and NL being split into divisions in 1969, the team with the best regular-season win-loss record in each league automatically clinched its league's pennant and advanced to the World Series, barring a tie necessitating a pennant playoff. Since then, each league has conducted a championship series (ALCS and NLCS) preceding the World Series to determine which teams will advance, while those series have in turn been preceded by division series (ALDS and NLDS) since 1995 and by wild card games in each league since 2012. The World Series has been contested 117 times as of 2021, with the AL winning 66 and the NL winning 51.
Until 2002, home-field advantage in the World Series alternated from year to year between the National League and American League. From 2003 to 2016, home-field advantage was given to the league that won that year's All-Star Game. Starting in 2017, home-field advantage was awarded to the league champion team with the better regular-season win-loss record, except in 2020, when a neutral-site ballpark hosted all games of the series.