The Boston Red Sox are an American professional baseball team based in Boston. The Red Sox compete in Major League Baseball (MLB) as a member club of the American League (AL) East division. Founded in 1901 as one of the American League's eight charter franchises, the Red Sox' home ballpark has been Fenway Park since 1912. The "Red Sox" name was chosen by the team owner, John I. Taylor, c.1908, following the lead of previous teams that had been known as the "Boston Red Stockings", including the forerunner of the Atlanta Braves. The team has won nine World Series championships, tied for the third-most of any MLB team, and has played in 13 World Series. Their most recent World Series appearance and win was in 2018. In addition, they won the 1904 American League pennant, but were not able to defend their 1903 World Series championship when the New York Giants refused to participate in the 1904 World Series.

The Red Sox were a dominant team in the new league, defeating the Pittsburgh Pirates in the first World Series in 1903 and winning four more championships by 1918. However, they then went into one of the longest championship droughts in baseball history, dubbed the "Curse of the Bambino" after its alleged inception due to the Red Sox' sale of star player Babe Ruth to the rival New York Yankees two years after their World Championship in 1918. The Sox endured an 86-year wait before the team's sixth World Championship in 2004. The team's history during that period was punctuated with some of the most memorable moments in World Series history, including Enos Slaughter's "mad dash" in 1946, the "Impossible Dream" of 1967, Carlton Fisk's home run in 1975, and Bill Buckner's error in 1986. Following their victory in the 2018 World Series, they became the first team to win four World Series trophies in the 21st century, with championships in 2004, 2007, 2013 and 2018. The team's history has also been marked by the team's intense rivalry with the New York Yankees, arguably the fiercest and most historic in North American professional sports.The Red Sox are owned by Fenway Sports Group, which also owns Liverpool F.C. of the Premier League in England. They are consistently one of the top MLB teams in average road attendance, while the small capacity of Fenway Park prevents them from leading in overall attendance. From May 15, 2003, to April 10, 2013, the Red Sox sold out every home gamea total of 820 games (794 regular season) for a major professional sports record. Both Neil Diamond's "Sweet Caroline" and The Standells' "Dirty Water" have become anthems for the Red Sox.As of the end of the 2021 season, the franchise's all-time regular-season record is 9,7189,014 (.519).

Baseball is a bat-and-ball game played between two opposing teams, of nine players each, that take turns batting and fielding. The game proceeds when a player on the fielding team, called the pitcher, throws a ball which a player on the batting team tries to hit with a bat. The objective of the offensive team (batting team) is to hit the ball into the field of play, allowing its players to run the bases, having them advance counter-clockwise around four bases to score what are called "runs". The objective of the defensive team (fielding team) is to prevent batters from becoming runners, and to prevent runners' advance around the bases. A run is scored when a runner legally advances around the bases in order and touches home plate (the place where the player started as a batter). The team that scores the most runs by the end of the game is the winner.

The first objective of the batting team is to have a player reach first base safely. A player on the batting team who reaches first base without being called "out" can attempt to advance to subsequent bases as a runner, either immediately or during teammates' turns batting. The fielding team tries to prevent runs by getting batters or runners "out", which forces them out of the field of play. Both the pitcher and fielders have methods of getting the batting team's players out. The opposing teams switch back and forth between batting and fielding; the batting team's turn to bat is over once the fielding team records three outs. One turn batting for each team constitutes an inning. A game is usually composed of nine innings, and the team with the greater number of runs at the end of the game wins. If scores are tied at the end of nine innings, extra innings are usually played. Baseball has no game clock, although most games end in the ninth inning.

Baseball evolved from older bat-and-ball games already being played in England by the mid-18th century. This game was brought by immigrants to North America, where the modern version developed. By the late 19th century, baseball was widely recognized as the national sport of the United States. Baseball is popular in North America and parts of Central and South America, the Caribbean, and East Asia, particularly in Japan, South Korea, and Taiwan.

In the United States and Canada, professional Major League Baseball (MLB) teams are divided into the National League (NL) and American League (AL), each with three divisions: East, West, and Central. The MLB champion is determined by playoffs that culminate in the World Series. The top level of play is similarly split in Japan between the Central and Pacific Leagues and in Cuba between the West League and East League. The World Baseball Classic, organized by the World Baseball Softball Confederation, is the major international competition of the sport and attracts the top national teams from around the world.