1940 Major League Baseball season

The regular season ended on September 29, with the Cincinnati Reds and Detroit Tigers as the regular season champions of the National League and American League, respectively.

The Reds defeated the Tigers, four games to three, capturing their second championship in franchise history, since their previous in 1919.

The eighth Major League Baseball All-Star Game was played on July 9, hosted by the St. Louis Cardinals at Sportsman's Park in St. Louis, Missouri, with the National League winning, 4–0.

Opening Day, April 16, featured all sixteen teams, the first since the 1936 season.

The 1940 season saw the following rule change: An asterisk (*) denotes the ballpark a team played the minority of their home games at 1 American League Triple Crown pitching winner