The 1921 World Series was the championship series in Major League Baseball for the 1921 season. The 18th edition of the World Series, it matched the National League champion New York Giants and the American League champion New York Yankees.

The World Series is the annual final championship series of Major League Baseball (MLB) in the United States and Canada. It has traditionally been held in October, though some more recent editions were contested in November due to expanded playoffs and/or season delays. It has been 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.