The 1919 World Series was the championship series in Major League Baseball (MLB) for the 1919 season. The 16th edition of the World Series, it matched the American League champion Chicago White Sox against the National League champion Cincinnati Reds. Although most World Series have been of the best-of-seven format, the 1919 World Series was a best-of-nine series. MLB decided to try the best-of-nine format partly to increase popularity of the sport and partly to generate more revenue.

Major League Baseball (MLB) is a professional baseball league and the highest level of organized baseball in the United States and Canada. One of the big four major leagues, MLB comprises 30 teams, divided equally between the National League (NL) and the American League (AL), with 29 in the United States and 1 in Canada. Formed in 1876 and 1901, respectively, the NL and AL cemented their cooperation with the National Agreement in 1903, making MLB the oldest major professional sports league in the world. They remained legally separate entities until 2000, when they merged into a single organization led by the Commissioner of Baseball. MLB is headquartered in Midtown Manhattan.