The 1969 Major League Baseball season was contested from April 7 to October 16, 1969. It included the third Major League Baseball expansion of the decade, with the Kansas City Royals, Montreal Expos, San Diego Padres, and Seattle Pilots each beginning play this season. The season was also celebrated as the 100th anniversary of professional baseball, honoring the first professional touring baseball team, the Cincinnati Red Stockings of 1869.
This was the first season of the "Divisional Era". With each league expanding from 10 teams to 12 teams, both leagues were divided into two six-team divisions. Teams continued to play 162-game schedules, in place since 1962, by now playing the other five teams in their own division 18 times each (90 games) and playing the six teams in their league's other division 12 times each (72 games). The winners of each division would advance to the postseason and face each other in a League Championship Series, then a best-of-five series, to determine the pennant winners that would face each other in the World Series.
The Baltimore Orioles won the AL East with an MLB-best 109–53 record, and then defeated the AL West champion Minnesota Twins in three games in the first American League Championship Series. The New York Mets won the NL East division with an NL-best 100–62 record, and then defeated the NL West champion Atlanta Braves in three games in the first National League Championship Series. The "Miracle Mets", having joined the league in 1962, were the first expansion team to win a pennant.
The upstart Mets went on to upset the heavily favored Orioles in the World Series, four games to one, in what is considered one of the greatest upsets in World Series history.