The 2004 World Series was the 100th edition of Major League Baseball's championship series. It featured the American League (AL) champions Boston Red Sox against the National League (NL) champions St. Louis Cardinals. The Red Sox defeated the Cardinals by four games to none in the best-of-seven series, played at Fenway Park and Busch Memorial Stadium. The series was played from October 23–27, 2004, broadcast on Fox, and watched by an average of just under 25.5 million viewers.

The Cardinals earned their berth into the playoffs by winning the National League Central, and had the best win–loss record in the National League. The Red Sox won the American League wild card to earn theirs. The Cardinals reached the World Series by defeating the Los Angeles Dodgers in the best-of-five National League Division Series and the Houston Astros in the best-of-seven Championship Series (NLCS). The Red Sox defeated the Anaheim Angels in the American League Division Series. After being down three games to none to the New York Yankees, they came back to win the 2004 American League Championship Series (ALCS) and advanced to their first World Series since 1986. The Cardinals made their first appearance in the World Series since 1987. The Red Sox won the World Series for the first time since 1918. With the New England Patriots winning Super Bowl XXXVIII, the World Series made Boston the first city to have Super Bowl and World Series championship teams in the same year (2004) since Pittsburgh in 1979.