The New York Yankees–Boston Red Sox rivalry is one of the oldest rivalries in American professional sports. For more than 100 years, Major League Baseball's Boston Red Sox and New York Yankees of the American League have been intense rivals. The rivalry is sometimes so polarizing that it is often a heated taboo subject, like religion orpolitics, in the BosWash region.

Since the inception of the wild card team and an added Division Series, the American League East rivals have squared off in the American League Championship Series three times, the Yankees winning twice in 1999 and 2003, and the Sox winning in 2004. In addition, the teams have met in the last regular season series of a season to decide the title in 1903 (where the Red Sox won) and 1949 (where the Yankees won). The teams also finished tied for first in 1978, when the Yankees won a high-profile one-game playoff for the division title. The 1978 division race is memorable for the Red Sox having had a 14-game lead over the Yankees at one point in the season.

Historically, the Yankees have had far more success. However, since the Red Sox' victory over the Yankees in seven games in the 2004 American League Championship Series, the rivalry has changed to a different direction, as the Red Sox have won two World Series during that time.